Trad Gang
Main Boards => Dangerous Game => Topic started by: Dr. Ed Ashby on September 03, 2010, 08:51:00 AM
-
The newest Update is posted. It contains information on how the penetration of an Ultra-EFOC arrow that is barely above the heavy bone threshold in mass compares to multiple other arrow groupings, including the super-heavy, classic buffalo arrows. Interesting results that might require some re-thinking of heavy game arrow setups.
Ed
-
thanks ed! can you post a link here so we can go straight to it?
now i'm off for some saturday morning reading. ha
-
also would you mind going into more detail on how you made and tuned a 31.4% UFOC arrow? :confused:
-
Clint, The arrow setup is in the Current Part 4 Update. Here's the link to it and to the Part 5 Update.
http://www.tradgang.com/ashby/2008update4.pdf
http://www.tradgang.com/ashby/2008update5.pdf
Ed
-
gee, thanks ed.
didn't know you had already put that info up.
cheers. :notworthy:
-
Well done again Doctor Ed. Nothing beats a careful and complete study. You should be in line for another degree or two! The debates that float about are interesting but solid data and caution cannot be beat. Good on you.
chrisg
-
Thank you again for such selfless dedication to our sport and traditions. Your commitment in the face of such relentless commercialization of speed to merchandize product is amazing, and I might add starting to make even the compound guys take note. I've seen you studies mentioned in more than one "wheelie" publicaiton this year.
I find it astonishing when people argue against your findings with no facts and no understanding of the underlying science.
-
As always, a pleasure and a privilege to read your reports.
Thank you Dr Ed.
-
two holes are always better than one.
Great stuff, Ed.
-
Excuse if these Q’s seem a little dull. Also thanks for clarifying the centre shot so simply.
Does this turbulator riffle the air over and down to the base of the feathers, is that what the A&A system is about?
Surely 4 feathers weigh very little but I imagine that’s integral to EFOC and grabbing the air as in more traditional FOC is not part of the equation as penetration with less force is the goal!?
If the shots were shorter, say half the distance would u be utilizing higher feathers or are these shafts sufficiently well tuned an rely on the EFOC pulling them to point. If longer would rainbow shot be required with EFOC?
R u indicating more speed in trajectory with higher EFOC?
Is it correct the tests would me even more forgiving with significant better result on live animal? As dead weight with lungs deflated there is no stretching of the bone and skin outward?
Thanks for enlightening Doc
-
Divecon, the Turbulator disrupts the air flow, which increases the pressure exerted by the air on the fletching. This increases the stabilizing effect of the fletching, which allows you to use a smaller amount of fletching to attain the same degree of stabilization in flight, but that is not the only purpose of the A&A fletching.
Using smaller fletching offers many benefits, and there's a pretty comprehensive thread about the A&A fletching. Here's the link. http://tradgang.com/noncgi/ultimatebb.php?ubb=get_topic;f=1;t=057257#000000
On an arrow that is already well tuned (correctly bare shaft tuned), using the minimum fletching required to overcome the wind shear created by the broadhead gives a higher FOC. As one approaches the level of Ultra-EFOC reducing shaft weight at the arrow's rear becomes a major factor in the degree of FOC change you and attain.
Ultra-EFOC is (Study defined) as being 30% and above. The reason being, it's really difficult to reach 30% and above FOC without making a concentrated effort to attain FOC.
Just putting high tip weight on most light weight shafts will get you into the EFOC range, but the higher the FOC gets the more increase in tip weight it takes to make the same degree of FOC increase. As Ultra-EFOC is approached it is more 'productive' to be reducing weight at the shaft's rear than adding additional tip weight. That's because the rear leaver arm (the distance from the nock to the balance point) gets longer as the FOC increases, and the forward lever arm, from the arrow's front to the balance point) gets shorter. The longer the leaver arm the more force a given amount of weight will exert.
As for close shots, a well tuned Ultra-EFOC bare shaft will recover from paradox incredable rapidly; it will certainly be showing straight impact into the target within 3 yards, and usually at even closer ranges. By adding a broadhead and then the minimum fletching required to overcome the broadhead's wind shear effect equally rapid recovery from paradon is retained. That's one of the things I most like about EFOC and Ultra-EFOC arrows; they show faster paradox recovery than normal or high FOC arrows, giving greater penetration on close range shots.
As for longer range shots, because EFOC/Ultra-EFOC arrows recover from paradox much more rapidly than normal/high FOC arrows, and the smaller fletching required to stabalize the broadhead in flight has less surface area, they have less drag. The rapid paradox recovery means less of the bow-derived energy of the arrow is wasted by paradox. As the arrow proceeds downrange, the smaller fletching not only has less drag it drains less energy when any flight correction is required. Because the EFOC/Ultra-EFOC arrow has a longer 'rear leaver' (or rear stearing arm, if you prefer) the fletching requires less 'applied force' to overcome any flight instability required by such things as the broadhead's wind shear and changes in air flow/pressure caused by changes in wind direction. All this retained arrow energy is now used to produce 'productive work'; higher retained arrow velocity and arrow force.
If you take 2 broadhead-tipped arrows that are identical in all external dimensions (except for the fletching, as the lower FOC arrow will require more fletching to overcome the broadhead's wind shear), and of equal mass (weight) and equally well tuned but having a large difference in FOC and shoot them at longer ranges you will see a very noticable difference in trajectory. The arrow having very high FOC will shoot noticable flatter. This is because of the additional 'useful energy' the arrow has attained from the bow and retained as it traveled downrange. Make up 2 such arrows yourself; one at normal FOC and one at EFOC and try that simple test at 40 meters or so. The difference in trajectory is very noticable.
In the Study's testing, all test shots are conducted within 30 minutes of the animal expiring. That's because early testing showed a difference between the results from shots taken on very fresh tissues and those taken after the animal had been dead for a longer period of time. Starting in 1982 I began to keep a seperate detailed database of each big game, bow killed animal. This information is used as a cross reference between the results observed on the test shots and the outcomes observed on real hunting shots. While the bow killed database has only 629 animals, whereas the test shot database(s) contains thousands, there is excellent correlation between the shot outcomes between the test shots and the actual bow kills. I wish I had started that bow killed database 25 years sooner, with my first deer. It would be very interesting to have the performance of those early arrow setups to also compare against.
Hope that helps a bit,
Ed
-
Originally posted by Dr. Ed Ashby:
While the bow killed database has only 629 animals, whereas the test shot database(s) contains thousands
Ed
Doc...wow I can't even imagine the dilligence, hard work and committment this has taken. I am amazed and grateful.
:notworthy:
-
Chop, Knowing how closely some folks seem to pour over everything I write looking for even the tiniest discrepancies :banghead: I went back and checked, and my database of bow-killed animals, excluding small game, has only 627 animals in it, not 629. Now that the record has been set straight I feel much, much better. :)
Ed
-
i'm glad you cleared that up for us Dr. Ashby! :) Good stuff!
-
That's it, now I have to question everything I've read!!!!! :p
Thanks again for everything you contribute to our understanding of terminal arrow performance. It has been eye opening and in many ways an epiphany.
-
Certainly helped thanks! Doc, In those early days, 82, were u considering EFOC or has this been a recent and experimental development. And is there reference to u’r 115# or other heavy bows and varying broadhead setups? Also info on u’r stat sheets
Cheers
[email protected]
-
Divecon.....click below and you can see where the question originated....right here on Trad Gang....and note the date of the thread....Pretty cool huh?
EFOC precursor (http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=39;t=000380#000000)
-
Devicon, Terry answered the FOC question! As you can see on that thread I was sceptical of the greatly improved penetration some folks were reporting with higher levels of FOC (as I am of most things based on casual observations, until I can test them and record the results ACROSS A LARGE NUMBER OF 'OUTCOMES'). Though I'd given FOC a bit of serious consideration because of what folks like Bob Morrison were reporting I had a lot of other arrow design factors I was already busily testing and FOC was sort of sitting on the back burner. It was Terry's thread that prompted me to move that testing forward.
My most commonly used arrow setup when the kills database was initiated was a Forgewood shaft with either the 190 grain Grizzly, Modified grizzly, Grizzly Extreme or Pearson Deadhead broadhead. That setup was an outgrowth of the Natal testing and the subsequent testing on cape Buffalo. Until the FOC question arose I had never even checked the FOC of that outstanding-performing setup. The FOC turned out to be just over 19%; just barely into the EFOC range. Looking back, I wasn't attributing nearly enough of the performance I was achieving with that setup to the arrow's FOC.
The kills database does include the few animals taken with the #115 pound longbow, and a few others taken with 100#+ longbows, but cumulatively those 100#+ bows total only a handful of animals.
Seems like the Field Data Recording Sheet and Study Protocols are not among the documents listed on TG. Here's a link where you can see them. http://www.tradbow.com/members/programs/fileinfo.cfm?id=10&action=display
Ed
-
Doc,thanks for all the work that you do.It has certainly forced me to look at things differently after doing things the same way for 45 years.
I recently bought some Victory V Force caron shafts in .300 spine to experiment with.have you tried these?They are much lighter than the Gold tips,with slightly less outside diameter but the same inside diameter.So far,they seem to be every bit as tough as the Gold Tips and very consistent.The .300 Victory V Force,so far,seem to be stiffer than the Gold Tips however.
Victory V Force shafts
.400- 6.2 gpi,.282 OD
.350- 6.7 gpi,.284 OD
.300- 6.9 gpi,.287 OD
-
Originally posted by JimB:
Victory V Force shafts
.400- 6.2 gpi,.282 OD
.350- 6.7 gpi,.284 OD
.300- 6.9 gpi,.287 OD
JimB,
I use those same shafts and I don't mean to nit pick, but those are the VFORCE HV shafts which are thinner walled than the regular VFORCE shafts which are more comparable to the gold tips dimensionally.
In fact someone here told me about them on my very first post here...was that you?
BTW these make it much easier to break 30% FOC. Only draw back to these shafts that I can see is that the raw shafts are only 31" which wouldn't work for very long draw lengths.
I use the V6s (+/- 0.006") which are affordable as carbons go for my practice arrows and use the V3s (+/- 0.003") for my hunting shafts.
-
Thanks very much chopx2.I did leave out the HV and that makes a difference.
I don't think it was me that told you about them.I learned about them from a member here also and was wondering if it were you.You can see my memory isn't that good.
The 3's are what I have and my preferred length is 29" so they work well and FOC is over 31 %.
I plan to order some .350's for a different setup.
-
DR Ashby, I have been reading and taking notes on all of your work and I have been very impressed. To late in the year foe me to make big changes to my setups. But I take 6weeks off from shooting after Dec, I plan on putting your results and findings to my benifit. Thanks for all of your work for all of us
-
Fantastic information, thank you for all your work.
-
Dr. Ashby.
Thanks for the new data and all your hard work. I am presently working up some hog and buffallo arrows and will be making sure they are somewhere in the 700 grain weight range with 400+ of that up front. I am figuring on getting high 20% to low 30% FOC. I have a trip planned to Oz next year and hope to put the hurting on some big pigs and maybe even a buff or scrub bull while there.
-
That was a good thread of informed opinion Terry, Bit of déjà vécu for ya. Also found Mr Nails formula interesting!
Doc u suggest that the approx 19% FOC set up was outstanding performance for u’r heavy bows . I imagine getting into the higher EFOC range is not as critical as it would be to enhanced performance of lesser weighted bows as the impetus is conducive of upper range draw weight. If/is that’s a fair assumption would u be inclined to repeat the same set up in the field, given the option, rather than apply EFOC? Assuming u were on the game instead of researching.
Is there any chance of getting that Field Data Recording Sheet and Study Protocols over on to TG?
Ta Doc
-
Dr. Ashby,
A question. I ended up with some very suprising ( to me ) results in the final arrows I ended up with for hunting. I am shooting 564 grain arrows - Easton Epic 600 spine shafts - with 400 grains up front. Grizzly El Grande broadhead - 125 grain steel adapter - aluminum insert and aluminum outsert. I am using a fletch tape - 5 inch and 4 - 3 inch fletch. The bow is a 68 inch Wes Wallace Royal longbow and pulls 55lbs at my 30.25 inch draw. The riser is 3/16 short of center cut. I started with 340 spine shafts, skipped 400 spine, tried 500 spine, and finally ended up at 600 spine arrows to get my arrows and bow tuned perfectly. The arrows actually ended up lighter than what I wanted.
Would you expect to need that light of a spine for the EFOC to work? I am thinking the short of center riser cut may be it.
I am working up some hog and buffallo arrows for a trip to Oz and plan to add another 50 to 100 grains to the 500 spine FMJ's I was working with to get them to tune right with my bow. This should put them right at 700 grains and around 25% FOC.
-
Dr. Ashby,
Thanks for all the real-world info ... truly insightful and much appreciated.
-
Clay, the degree of centershot a bow has is a HUGE factor in the dynamic spine required for the arrow to bare shaft tune correctly. I've found much the same results as you show. I have one (far from centershot) 85# bow that tuned with a 40-55 shaft, with 415 grains of point weight.
There are a lot of factors that affect what dynamic spine your bow will require. Each is an individual, but altering the degree of centershot is a major tuning factor that you can use to your advantage when trying to develop EFOC and Ultra-EFOC arrows.
Divecon, I've sent copies of the Field Record Data Sheet and Study Protocols and the Blood Trail Data Sheet to the TG Webmaster today, to see if they can be posted on the library here. Hopefully they will be in a downloadable format. I especially hope that a few folks will complete and submit their own information on the Blood Trail Data Sheet. A HUGE amount of blood trail data will be needed before there will be any statistical significance to the results.
As to my own hunting arrow setup, the first consistantly measurable increase in real-tissue penetration between arrows of otherwise equal dimensions shows up at 19% FOC. All else equal between 2 arrows, as the difference in FOC increases above 19%, penetration increases at what appears to be an ever increasing rate of penetration gain per one % change in FOC. In other words, the penetration gain per 1% FOC increase gets greater the higher the FOC gets.
I had very good field success on big game for years with arrows in the 800 grain range at just over 19% FOC; all from fairly heavy draw weight bows. After getting into the EFOC/Ultra-EFOC testing and seeing the results I immediately changed the setup of my 'serious hunting arrows' to an EFOC setup, and am now moving them into an Ultra-EFOC setup.
Unlike some, I am not content to take the position that the arrow setup that has worked satisfactorily for me for years is 'good enough'. There are so many things that can happen when one is shooting at an animal. Regardless of how good a shot one is, and how hard one tries to make a perfect shot on each animal, under actual hunting conditions it's impossible to predetermine exactly where your arrow is going to impact, and what you MIGHT be asking your arrow to do if you are to successfully recover the animal. No hunting arrow can ever work 'too good'. Whenever the testing shows me that I can improve on the terminal performance of my hunting arrow in any way I will do so. For hunting I want the very best performing arrow setup I can possibly be using; the one that gives me the highest possible chance of success, regardless of what the hit turns out to be. In bowhunting there is no such thing as overkill.
Ed
-
Originally posted by Dr. Ed Ashby:
Clay, the degree of centershot a bow has is a HUGE factor in the dynamic spine required for the arrow to bare shaft tune correctly....
In other words, the penetration gain per 1% FOC increase gets greater the higher the FOC gets.
Dr. Ashby, I had a few questions I was hoping you could expound on.
1. On the centershot topic I have experienced the same thing, Have you also experienced any erratic flight "stiff-like" issues if the long 100gr insert gets drawn back on to the riser? I believe i have experienced this, but can't be sure for lack of time to test.
2. Just a comment on the non-liners >19% FOC penetration increase - that is amazing!
3. Regarding the A&A fletching style. Do you start tuning with this set-up or do you use a bigger helical type fletch for initial tuning? I need to tune a new heavier bow and I was thinking of giving the A&A fletching a try.
4. I saw a post regarding using cut reflective wraps for the turbulator. Do you know if they work since they are thicker than the regular wraps? Still looking to find some pin striping tape locally, but have some wraps sitting around that would be a lifetime supply if they work.
5. Broadhead width. I know you get the best penetration on your modified 1" wide grizzlies. Do you attribute that all to the 3:1 mech adv or do you think the narrowness is a factor. I.e. would a 1x3 BH out penetrate a 1.5x4.5 BH (same MA) or what about 7/8 x 2 (less MA) vs 1 x 3? Would bone be different than soft tissues?
-
ashby record sheet pdf files (http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=24&t=000020)
-
Rob, thanks for getting those posted. I hope a few folks will take the time to fill out the Blood Trail Data Sheet and submit them. It's going to take a substantial amount of blood trail data to ever be able to come up with statistically meaningful results.
Chop, I’ll try to answer your questions point by point.
1. I’ve not noticed any problem with the longer inserts, when drawn onto the shelf, and a couple of my Ultra-EFOC shafts are at the very minimum length I can possibly use (simply because that’s the length the happened to tune at). I have encountered ‘false stiff spine’ with shafts that had a weak dynamic spine and were excessively long. In those instances the rear of the shaft was hitting the riser and causing the arrow’s flight to show a ‘too stiff’ point of impact. Shortening the shaft cures that, with the point of impact dropping from the ‘false stiff spine’ to showing a ‘weak spine impact’ and then, as the shaft is shortened more, a progressively stiffer dynamic spine until the shaft either tunes correctly or I run out of shaft length to shorten.
2. In the next Study Update there will be a detailed examination of what the data SUGGEST about the amount of penetration gain per percent increase in FOC; as FOC progressively increases.
3. I first bare shaft tune the shaft with a field point of matching weight and assemblage (same weight field point as the broadhead I am planning to use, same type and weight BH taper, if one is used, same insert, same internal footing, if one is used).
In my bare shaft tuning what I’m looking for in the un-fletched shaft is: (a) visually perfect flight (no wiggles, wobbles, flips, flops or flaps); (b) Fast recovery from paradox. I want the bare shaft showing straight impact into a uniform medium target by AT LEAST the time it reaches a distance of 3 yards – and often they will show straight line impact at distances as close as 3 feet – and I want it to maintain that straight impact at all distance back to 40 meters. This needs to be tested under calm wind conditions by shooting at each yardage back to 40 meters. (c) I want the point of impact at 40 meters to show only a very slight weak spine impact; no more than 2 to 3 inches right (for my right hand shooting; it should be left for a ‘lefty’).
Once I have a given EFOC or Ultra-EFOC arrow bare shaft tuned to my satisfaction I then fletch one of the field points up and verify that the fletched shaft shows matching flight against the bare shaft. On EFOC and Ultra-EFOC shaft I use 3 inch, parabolic cut four fletch on this test shaft. On normal/high FOC arrows I will use either 4 inch or 5 inch four fletch for this test shaft, depending on arrow FOC. This fletched, field point tipped shaft should now show perfect flight and impact ‘dead on’, left to right, at 40 meter.
Next I place a couple of the broadheads I will be using onto the shafts and fletch them up and check the flight against the bare shaft. I use the same ‘starting size’ fletching as I used on the fletched field points shaft. If all looks good with the broadhead’s flight I shift over to a ½” high, A&A pattern cut (without the turbulator) and begin to gradually reduce the size (total surface area) of the fletching until the first place I see a TINY AMOUNT OF INSTABILITY in the flight of the broadhead tipped arrow. At that point I add the turbulator, placing it 1/4" in front of the fletching. Almost always the turbulator immediately creates enough increase in air pressure on the fletching to again fully stabilize the broadhead's flight. If it doesn't, with the turbulator consistently maintained at ¼” forward of the fletching, I begin increasing the length of the fletching in 1/8" steps, maintaining the ½” fletching height, until I'm fully satisfied that the flight is stable.
When testing flight stability with the broadheads be sure to shoot a good number of shots, and I like to shoot the broadheads multiple times under various wind conditions (into the wind, with a trailing wind, cross wind and both into and with a quartering wind) until I'm totally satisfied that the fletching will stabilize the broadhead flight in all wind conditions, even when I get a less than clean finger release.
This sounds like a lot of work, but really isn't as bad as it sounds. After you do a few you get a pretty fair idea of what it takes for your individual shooting style and a particular broadhead. It goes fast after that, as you can often ‘shortcut’ the steps, based on previous experience. For example, I now know that, for arrows with an FOC above 25% FOC and a relatively ‘low wind sheer broadhead’, I can start out with 2.5”, four fletched, A&A cut-pattern feathers.
As well as the amount of FOC your arrow has, the amount of fletching (total surface area) you'll need is also dependent on the length of the arrow's rear steering arm. At any given amount of FOC, the longer your arrow’s shaft, or the closer your fletching is to the nock, the less fletching (total surface area) that is required. At any given amount of FOC, the shorter your arrow, or the further forward (in front of the nock) the fletching is placed, the more fletching required.
Here's a link to the TG thread on Fletching and EFOC. There's some information in there that may be of use.
http://tradgang.com/noncgi/ultimatebb.php?ubb=get_topic;f=1;t=057257#000000
4. I have not tried the reflective tape but other folks that have say it works as well as the pinstripe tape. Best thing to do is top try it yourself and see how it works for you. I’m just a bit too lazy to cut the tiny, uniform width strips out. The pinstripe tape is just cut to length, peal and stick, securing the cut-end juncture with a thin smear of glue. Most hobby supply stores have the pinstripe tape.
5. As far as penetrating heavy bone, from the Study data the true critical point of broadhead Mechanical Advantage (MA) appears be 2.6, not 3.0. In the 2007 Update, Part 4, you can find a more complete discussion, in the sections titled The Importance of High Broadhead MA and Another Look at Broadhead MA’s Effect. Here’s the link.
http://www.tradgang.com/ashby/2007update4.pdf
But there is one important thing to note; don’t confuse a 3.0 MA broadhead with what some folks term a “3 to 1 ratio” broadhead. With a single-blade broadhead, a “3 to 1 ratio” broadhead – that is, one that has a TOTAL cut width of 1” wide and a cutting-edge length of 3” - WILL have a MA of 3.0; but that’s not how some folks interpret “3 to 1 ratio” when it comes to multi-blade broadheads. Some folks seem to interpret “3 to 1 ratio” to mean that the height of each cutting blade is 1/3 the length of that blade’s cutting edge. For example, some folks will term a three-blade broadhead where each blade had a cut height of ½” with a cutting edge length of 1.5” a “3 to 1 ratio” broadhead; meaning that the cutting edge of that individual blade is three times the height of that individual blade. This gives THAT INDIVIDUAL BLADE a MA of 3.0, but it DOES NOT give the broadhead a MA of 3.0. The overall MA of such a broadhead is only 1.0! That’s because the total cut width of 1.5” equals the 1.5” length of the broadhead’s cutting edge.
It’s important to note that the data shows that ALL structurally intact, ‘above the heavy bone threshold’ arrows having broadheads with an MA above 2.6 penetrated the entrance side ribs in the buffalo testing; regardless of whether the broadhead was of single-bevel or double bevel design. The big difference between single-bevel and double bevel broadheads comes in the average amount of penetration achieved AFTER THE BONE WAS PENETRATED. Every 2.6 MA (and above) single-bevel broadheads showed greater average post-breaching penetration the ANY comparable double-bevel broadhead. Bevel type and design are major factors in breaching heavy bone; using less of the arrow’s ‘useful energy’ during bone breaching and retaining more of the arrow’s force for post-breaching penetration of the underlying tissues. A clear example is shown in the 2007 Update, Part 4, in the section titled Another Look at Single-Bevel vs. Double-Bevel Broadheads. There, the penetration outcomes of arrow setups that were identical, excepting only the broadhead’s type of edge bevel, are compared. Here’s that link: http://www.tradgang.com/ashby/2007update4.pdf
More specific to your question, in ‘all soft tissue hits’ testing the very narrow, very high MA (11/16” wide) Grizzly Extreme out-penetrates both the somewhat lower MA, 1” wide, Modified Grizzly and the still lower MA, production-profile, 190 Grain Grizzly. When tested on heavy bone hits that MA relationship does not produce the same outcome. There the Modified Grizzly out-penetrated both the narrower Grizzly Extreme and the wider-cut 190 grain Grizzly.
Heavy bone penetration becomes a balancing act, especially for the single-bevel broadheads. For penetrating heavy bone with single-bevel broadheads there is definitely a broadhead width factor involved. The wider a broadhead is (at a given length) the lower the broadhead’s MA, and the more arrow force required to penetrate the bone, but with the single-bevel broadheads there are off-setting factors. With single-bevel broadheads, the broadhead’s width affects the length of ‘lever arm’ for the lateral torque created by pressure differential of the bone (or other tissues) on the edge-bevel’s surface. Due to the differing angle of attack, broadhead width also affects the amount of surface area the edge-bevel will have in contact with the bone at any given instant during penetration.
The angle of the edge-bevel that you have applied to the broadhead also affects the amount of edge-bevel surface area in contact with the bone at any given instant during penetration. Thickness and density of the bone are also factors, working inversely to what many would assume. The thicker the bone the more of the bevel’s surface area in contact with the bone at any given instant, which means a greater pressure differential on opposing sides of the single-bevel blade, resulting in greater lateral (rotational) torque. The denser the bone the greater the pressure exerted between the bone and the surface area of the single-bevel’s edge; resulting in a greater rotational pressure differential and greater rotational torque.
These conflicting forces; resistance due to broadhead MA and bone density and thickness vs. the broadhead’s ability to generate sufficient rotational torque to split that given bone; are a delicate balance. I know of no way other than relying on outcome driven results from a huge number of shot into real tissues to determine what broadhead design gives the best results on the greatest number of outcomes. You can read more about this topic at http://www.tradgang.com/ashby/2004update1.pdf and http://www.tradgang.com/ashby/single-bevel-broadheads.pdf
Hope that helps,
Ed
-
Doc, Thanks for taking so much time to provide such incredibly thorough and the great answers.
You were right about the weak spine. I didn't account for the amount of impact a center cut riser has. I Had to go to stiffer arrows. once i did that they now showed weak at full length and did some trimming of length and got close out to 20yds. Hope to continue the progress tomorrow.
Scarily the whole explanation about the single bevel vs, bone size and density actually makes sense. I've noticed that Large single bevel knives are harder to cut 'straight' with than some smaller steak knives I have of the same set.
i will re-read those studies as I cleary missed some important things in them.
Thank you again for everything!
-
Thanks Rob!
That appearance of penetration gain rate once beyond 19% FOC must be a revelation for many, over time.
Bugger! Just when one thinks he’s getting a clue, now a base understanding of something previously not considered.
Although enjoying the experimentation one also appreciates the opportunity to avoid some of the uncertainties
U’r bloods worth bottling Doc.
-
Not too sure about bottling my blood, Divecon. :scared: I got really sick, :( and have some lasting reminders of the encounter :bigsmyl:
Ed
-
Which spider and what does it look like? Headed to Oz next July and would love to avoid that particular species.
-
Hery you are, Clay.
http://www.csiro.au/resources/Funnelweb-Spider-Facts.html
and
http://www.duttcom.com/MiniBeasts/funnelweb.html
and
http://emedicine.medscape.com/article/772401-overview
and
http://emedicine.medscape.com/article/772401-treatment
That should get you started. Google for the Australian Red Back Spider too. Another pretty bad one that's commonly encountered.
Ed
-
What he’s not saying Clay is to get bit by that funnel web, by poking u’r appendages where there not welcome is usually the prerogative of researchers lookin for trouble. A side effect if u will, a bit like spiderman, is once the toxin has run its course and if the victim actually survives they are then semi immune to hypothermia as the blood has an anti freeze quality whereby they can sustain long periods in unusually cold conditions with the barest of clothing.
One thing u will notice when u come to OZ is that everyone leaves the toilet seat up! That ‘s not to upset the women. Women traveling from overseas should be aware that this is a small courtesy we ask, it’s simply that Red Back spiders live under toilet seats if indoors, in the dark. Stats from the 50’s show that when they started putting seats in thunderboxes there was a marked increase of attack.
-
I will bring that up to Tricia on the toilet seats and tell her I am practicing at home so I don't forget on our trip.
Dr. Ashby, Thanks yet aqain for your help and constant information sharing. I have found them to be immensely helpful and a thoroughly good read.
Divecon, so our saying Dr. Ashby can hunt in the winter in a loin cloth and he will be just fine? No freezing to death? :biglaugh:
-
Originally posted by divecon10:
A side effect if u will, a bit like spiderman, is once the toxin has run its course and if the victim actually survives they are then semi immune to hypothermia as the blood has an anti freeze quality
I ggogled it and IT"S TRUE! It even stated that in rare cases the victim even develops an uncanny ability to scale walls! :p
-
Amazingly complete study. One day I might understand it fully.
-
So I've got a little bit of a dilemna.....I can build one of two arrows here. One is slightly above heavy bone threshold at 661 grains and 28 % FOC in a thin diameter shaft or I can get a just under threshold, 615 grain total shaft in a standard carbon diameter at 30.6 % FOC. So which would be the "deal breaker" factor? Slightly higher FOC (into the ultra FOC realm) or just above heavy bone threshold (dang near ultra FOC)?
-
Crazyhorse
Option 1 thin shaft: reduce the rear lever arm.
What size and number of fletching do you use?
If you're not already try 3" low profile feathers on the 661gr arrow. This will increase your FOC. Doesn't take much grain weight off, but because the rear lever arm length each grain is magnified more in the back like a see saw. Search the A&A fletching thread. I think there is a link in this thread to it.
Option a 5/16 shaft: You can stiffen the shaft by building out the arrow side plate thus allowing you to add weight to the point increasing weight and FOC which will give you awesome FOC. I have to build out ALL my cut to center bows to achieve FOC even with .300 spine shafts. Right now I'm tuning a 58# at 29" L/B with .300 shafts and they are 32.6% FOC and still weak so tonight I'm going to build out the side plate even more (to about 1/4-3/16").
-
Here's one I encountered many years ago Clay,
(http://i306.photobucket.com/albums/nn273/andyabersoch/102_3881.jpg)
This particular Funnel web was able to walk under water and nearly crawled up my bare foot when I was fishing for Crayfish in a creek.
Sorry for the poor pic but looking at those fangs it gives you an idea what a bite from one of these would be like :scared:
They are residents of the Sydney area and Blue mountains, so if you are heading up North you will be Ok.
-
Wolf Kiss, we will be in the Mackay area and then rolling out into the outback for some hunting with an Aussie gentleman who was generous enough to offer up a stay at his place and hunting on some property he has access to. He and I both served in the military and in Iraq.
Tricia and I are really excited to be coming over for a visit in Oz. We have three weeks planned for the trip the last week of July and first two weeks of August next year.
-
Just looking at that picture made me shudder and I'm not squeamish. :scared:
-
Originally posted by Dr. Ed Ashby:
Clint, The arrow setup is in the Current Part 4 Update. Here's the link to it and to the Part 5 Update.
http://www.tradgang.com/ashby/2008update4.pdf
http://www.tradgang.com/ashby/2008update5.pdf
Ed
What does Arrow MA mean?
What would the effect of a 30% FOC be with a 900 grain arrow?
Much Aloha...
-
MA stands for "Mechanical Advantage". The MA of a "machine" is the ratio of the 'force input' to the 'force output'. (Note that this is a ratio of "Force", not a ratio of Kinetic Energy; yet another reason why KE isn't useful for predicting the 'work' your arrow can accomplish - i.e. the degree of penetration.)
Your broadhead is a 'simple machine', comprised of a series of inclined planes. Your broadhead comprises a part of the larger 'simple machine'; your arrow. Each has its own MA. The approximate MA of a broadhead is relatively simple to calculate. The overall MA of your arrow is more difficult to calculate.
The MA of a simple machine tells you how much the "applied force" is multiplied by use of that particular 'machine'. A MA of 3.0 multiplies the applied force by a factor of three, meaning it allows the applied force of your arrow to do 3 times that amount of "work", when applied against a given 'resistance load'. A word of caution: Don't confuse what some term a "3 to 1 ratio" broadhead with the broadhead's MA; not the same thing.
Hope that helps,
Ed
-
Woops, forgot the second part of your question. Here's what the testing indicates:
(1) At equal arrow weight and equal external arrow dimensions, the higher the FOC the greater the penetration.
(2) At equal arrow weight and equal external arrow dimensions, the higher the arrow's FOC the greater the degree of penetration gain PER EACH 1% OF FOC INCREASE.
(3) At equal external arrow dimensions and equal amounts of FOC, but with differing arrow weights, the greater the arrow weight the greater the average outcome penetration. The difference in average outcome penetration, percentage wise, will be PROPORTIONAL to the percentage of increase in the arrow's force. (Force is measuered by the arrow's momentum. An arrow's 'energy' is not a measure of the arrow's force.) For example: At equal external arrow dimensions and equal amounts of FOC, but with differing arrow weights, the percent increase in the arrow's momentum is closely equivalent the percent of increase in the average outcome penetration; when measured across a large number of shots into real tissues. Often the percentage increase in average penetration will slightly exceed the increase in arrow force. Why? The increased arrow force is being applied by a 'simple machine', which can multiply the arrow's force increase.
BTW: Not every broadhead on the market has a MA exceeding 1.0, though most traditional broadheads do. A broadhead with a MA below 1.0 REDUCES the 'work output' an arrow carrying a given amount of force can do. When measured across a large number of shots into real tissues, increasing arrow force by a given amount, WHILE USING A BROADHEAD WITH A MA BELOW 1.0, results in an average penetration increase SIGNIFICANTLY LESS than the percentage of increase in arrow force.
Ed
-
Never thought I would get a physics lesson on an archery forum, LOL! Thanks for the great info and work you do Dr. Ed! :thumbsup:
-
Dr. Ashby...where were you freshman year!
I might have gotten better grades if they applied physics to something I cared about like bowhunting!
-
Hi Dr. Ed....
Ok... here goes.... :)
1) How do you calculate the MA of a Broadhead or is it published in your wonderful works.
2) Arrow weight and FOC... You said that a heavy arrow is as effective as a lighter (though heavy) arrow with a 30% FOC. You just now are saying that the FOC with 30% is commensurately better and so I'm assuming (I'm somewhat slower to have lights go off sometimes... ok.. maybe more often than that... )that a 700 to 900 grain arrow with a 30% FOC will have a commensurately greater penetration than an arrow somewhat more modest with 30%.
I've tried to explaine Kinetic Energy and Momentum to my kids in that Kinetic Energy might get it there, but momentum gets it done. What I mean by that is that as with heavy bullets, it doesn't matter how it gets there, it's what happens when it does, and it's the energy contained within the projectile that provides penetration.
I know a superfast arrow or bullet can sometimes provide enough speed to penetrate, but usually at the expense of a good wound channel.
I'm learning how to make arrows from some of the trees we grow here in Hawaii and that leaves me to anothter question for you...
It was you I think mentions that when the arrowshaft is smaller than the ferrule, then penetration is improved. I'm not sure how this works, even my wood arrows are tapered into the ferrule and the shaft itself is larger than the ferrule. However, the argument seems to be saying that a tapered shaft (FOC aside) might have better penetration.
-
Dang... something happened there.... Tapered shafts... what happens if you taper towards the arrowhead as well as towards the nock? Would that improve penetration any (again FOC notwithstanding)?
Much Aloha... :cool:
-
Rattus58,
The mechanical advantage of a wedge depends on the ratio of its length to its thickness. Where a short wedge with a wide angle does the job faster, it requires more force than a long wedge with a smaller angle. For the purposes of simple comparison of one broadhead to another, and assuming similar profiles for the ferrules on both broadheads, you can just use the MA of the main blade, which is a wedge. I borrowed the directions for the MA of a wedge from a University of Arkansas web site.
“The mechanical advantage of a wedge can be found by dividing the length of either slope (S) by the thickness (T) of the big end. As an example, assume that the length of the slope is 10 inches and the thickness is 4 inches. The mechanical advantage is equal to 10/4 or 2 1/2. As with the inclined plane, the mechanical advantage gained by using a wedge requires a corresponding increase in distance.” Note that that the “Slope” is the length ALONG ONE EDGE of the wedge. The “Thickness” would be the width of the broadhead.
Here’s what the Study data indicates about the FOC effect on average outcome penetration into tissues, expressed differently.With arrows having equal external dimensions (same broadhead, same shaft diameter and material), equal quality of arrow flight and total arrow integrity (remembering that FOC’s measurable penetration effect does not show up until a FOC of 19% is reached):
(1) Having a greater degree of FOC allows a lighter arrow to equal the penetration of a heavier arrow having a lesser amount of FOC. How much difference in weight there can be becomes a function of both the amount of FOC difference between the two arrows and the starting point for the FOC change (the FOC of the heavier, lower FOC arrow). That’s because the rate of penetration gain becomes greater the higher the FOC gets. In other words, a change from 30% to 31% FOC yields a greater penetration increase than does a change from 20% to 21% FOC, or from 26% to 27%. The upcoming 2008 Update, Part 6 will have an analysis of what the data suggest is the degree of change that can be achieved by Ultra-EFOC, as well as a brief review of what a similar analysis of the 2007 testing EFOC data indicated.
(2) When arrow FOC is equal but arrow weight is different the arrow having the greater weight will have greater penetration.
You definitely want the diameter of your arrow’s shaft to be less than the diameter of the broadhead’s ferrule. All else equal between two arrows, the difference in average outcome penetration between a shaft diameter smaller then the broadhead’s ferrule and a shaft diameter greater than the diameter of the broadhead’s ferrule is 40%. That’s HUGE!
When all else is equal between two arrows, a tapered shaft out penetrates a parallel shaft, and a parallel shaft out penetrates a barrel tapered shaft. Here’s where you can read more about this.
http://www.tradgang.com/ashby/2004update2.pdf
http://www.tradgang.com/ashby/2007update8.pdf
http://www.tradgang.com/ashby/Momentum%20Kinetic%20Energy%20and%20Arrow%20Penetration.htm
Hope that helps,
Ed
-
Dr. Ashby,
Not wanting to be obtuse (i.e. low MA [mental ability]) but I assume tapered meaning the larger diameter at the BH end of the arrow.
Do you know of any other tapered carbon shafts other than Grizzlystiks?
-
Originally posted by Dr. Ed Ashby:
Rattus58,
“The mechanical advantage of a wedge can be found by dividing the length of either slope (S) by the thickness (T) of the big end. As an example, assume that the length of the slope is 10 inches and the thickness is 4 inches. The mechanical advantage is equal to 10/4 or 2 1/2. As with the inclined plane, the mechanical advantage gained by using a wedge requires a corresponding increase in distance.” Note that that the “Slope” is the length ALONG ONE EDGE of the wedge. The “Thickness” would be the width of the broadhead.
(1) Having a greater degree of FOC allows a lighter arrow to equal the penetration of a heavier arrow having a lesser amount of FOC. How much difference in weight there can be becomes a function of both the amount of FOC difference between the two arrows and the starting point for the FOC change (the FOC of the heavier, lower FOC arrow). That’s because the rate of penetration gain becomes greater the higher the FOC gets. In other words, a change from 30% to 31% FOC yields a greater penetration increase than does a change from 20% to 21% FOC, or from 26% to 27%. The upcoming 2008 Update, Part 6 will have an analysis of what the data suggest is the degree of change that can be achieved by Ultra-EFOC, as well as a brief review of what a similar analysis of the 2007 testing EFOC data indicated.
(2) When arrow FOC is equal but arrow weight is different the arrow having the greater weight will have greater penetration.
You definitely want the diameter of your arrow’s shaft to be less than the diameter of the broadhead’s ferrule. All else equal between two arrows, the difference in average outcome penetration between a shaft diameter smaller then the broadhead’s ferrule and a shaft diameter greater than the diameter of the broadhead’s ferrule is 40%. That’s HUGE!
When all else is equal between two arrows, a tapered shaft out penetrates a parallel shaft, and a parallel shaft out penetrates a barrel tapered shaft. Here’s where you can read more about this.
http://www.tradgang.com/ashby/2004update2.pdf
http://www.tradgang.com/ashby/2007update8.pdf
http://www.tradgang.com/ashby/Momentum%20Kinetic%20Energy%20and%20Arrow%20Penetration.htm
Hope that helps,
Ed
Again, I cannot thank you enough. I've some wood drying right now that I'm going to cut into shafts. How would I, unless I cut the shaft to a smaller diameter to start with, effect with a wood arrow, a ferrule diameter smaller than my shaft. My Cedar/Ash shafts are 23/64" right now and the ferrules look like they are max maybe 5/16" maybe less even.... (Snuffers).
Will a taper from the Broadhead, as already asked, work to improve this situation... and how does a taper of the tail help if any?
Again, Thank you profusely for your insight and knowledge that you share with us...
Much Aloha,
Tom
-
Doc,
I asked this question a page or two back but am wondering what your personal preference would be. I can build two arrows that will tune perfectly for my set up . One is just under heavy bone threshold (about 620 grains with an FOC of right on 30%. The other is just over the threshold at 661 grains with a 28%foc. This is done with a axis 500 shaft, 100 grain insert, 300 grain broadhead vs. a beman mfx same insert same broadhead. If your choices were limited to these two shafts, which would you pick for game up to and including african plains species?
-
Oh yeah, and I've already switched to a bare minimum of wrapped cresting and a small RAYZR type feather so the only real variable in the set up is the model of shaft and the grains per inch.
-
AKCrazyhorse, for me, personally, the choice would be simple. I always try to plan for the worst hit that MIGHT occur. The heavy bone threshold has been so persistant in all testing that I won't hunt big game with an arrow below 650 grains. Though having higher FOC increases the arrow's penetration once a heavy bone is penetrated testing shows that the degree of FOC has no effect on the arrow weight required to breach a heavy bone. I'd use the 28% FOC, 661 grain arrow.
Ed
-
Good enough for me doc. thanks
-
Originally posted by Dr. Ed Ashby:
AKCrazyhorse, for me, personally, the choice would be simple. I always try to plan for the worst hit that MIGHT occur. The heavy bone threshold has been so persistant in all testing that I won't hunt big game with an arrow below 650 grains. Though having higher FOC increases the arrow's penetration once a heavy bone is penetrated testing shows that the degree of FOC has no effect on the arrow weight required to breach a heavy bone. I'd use the 28% FOC, 661 grain arrow.
Ed
Any thoughts on the wood arrow/ferrule dimension question?
Aloha...
-
Rattus58,
From my previous post:
You definitely want the diameter of your arrow’s shaft to be less than the diameter of the broadhead’s ferrule. All else equal between two arrows, the difference in average outcome penetration between a shaft diameter smaller then the broadhead’s ferrule and a shaft diameter greater than the diameter of the broadhead’s ferrule is 40%. That’s HUGE!
When all else is equal between two arrows, a tapered shaft out penetrates a parallel shaft, and a parallel shaft out penetrates a barrel tapered shaft.
Regardless of whether the shaft is parallel, tapered or barrel tapered, you never want the shaft's maximum diameter, at its widest point, to be greater than the diameter of the broadhead's ferrule. That applies regardless of the shaft material you are using. Doing so will cost you dearly in penetration. Ideally the shaft's maximum diameter should be AT LEAST 6% smaller than the diameter of the broadhead's ferrule.
Sorry I wasn't clearer on the first post,
Ed
-
Got it... now to figure out how cut my shaft diameters down or find a different broadhead than the snuffer...
Much Aloha... Tom
-
Chopx2-The Arrow Dynamics shafts are full length tapered.
-
Originally posted by slivrslingr:
Chopx2-The Arrow Dynamics shafts are full length tapered.
What does that mean... full length tapered?
Much Aloha... :cool:
-
The point end starts fat and tapers to skinny at the nock end. I'm not sure what the dimensions are.
-
Aren't the Grizzly Stics the same type of taper?
-
Hmmmmmm I guess if you can taper the tailshaft, you could figure out a full length tapering jig.. I'd be curious also in the tapering dimensions... like 23/64 to 5/16 or what?
Dr. Ashby suggests that this might be the ideal for penetration when you really need it...
Much Aloha... :cool:
-
The Grizzly Stiks are tapered from the nock all the way to the point end. I didn't see any dimensions, but I may have missed them. A six pack of those shafts is like buying a box of factory ammo for a 470 NE!
-
Originally posted by Andy Cooper:
The Grizzly Stiks are tapered from the nock all the way to the point end. I didn't see any dimensions, but I may have missed them. A six pack of those shafts is like buying a box of factory ammo for a 470 NE!
:biglaugh: The taper goes thick at the broadhead and skinny at the nock... right?
Much Aloha... :cool:
-
Yes, I didn't state that very well! The nock end is smaller diameter than the point end...like a baseball bat...sorta. More like a throwing dart.
If I'm understanding this EFOC biz correctly, then once the threshold for arrow weight, velocity, and FOC have been reached, then the only reason to go to a heavier draw weight is to be able to shoot a heavier arrow...right?
(Maybe I should quit reading between appointments so I can concentrate better!) :readit:
-
Haha.... I think quitting while you're ahead is good... :cool:
Aloha....
-
Oh... and thanks....
Aloha... :cool:
-
Can't quite now...I've dreamed of hunting cape buffalo for years. My dream is coming closer.
-
Originally posted by Andy Cooper:
Can't quite now...I've dreamed of hunting cape buffalo for years. My dream is coming closer.
That is my goal too for if not next year, the year after...
I'm told Buffalo is about $15,000 for the hunt, which is right at my limit unfortunately...
Plains game hunting there is cheaper and plentiful too, than an elk hunt.
Much Aloha... :cool:
-
You should look at coming to Oz and hunt water buff and pigs (lots of other critters as well). It's cheaper and likely just as much fun. That's what my plan is! :D
-
Originally posted by slivrslingr:
You should look at coming to Oz and hunt water buff and pigs (lots of other critters as well). It's cheaper and likely just as much fun. That's what my plan is! :D
That is something I'm considering doing, too! :archer:
-
With all the things I hear about how much you guys have down under, I 'm trying to talk her into moving!
BTW don't tell her about the spiders...shhhhhhhhhh :nono:
I'd love to take a buff there with my buffalo bow.
-
Has anyone built EFOC arrows using the Arrow Dynamics Heavy Hammerhead shafts?
-
I'm working with some regular HH's for my 69# recurve, but am having some issues as it appears they are too weak when full length (the tail kicks left during flight). I find that hard to believe as they are supposed to spine at about 90#. I'm running 360 grn. on the front. I'm hoping to get these arrows sorted and get after some buff next year. The Heavy's may be stiffer and able to handle more weight on the front, but I'm not sure what their spine is.
Yup, plenty of stuff to hunt here. One thing to keep in mind is that it's a big country and a long way to anything. While there are plenty of spiders and snakes that can cause issues, they pretty much keep to themselves, though being cautious never hurts!
-
On one of my bows my bare shaft tuning was telling me I needed stiffer spine. I was already at .300 with 415 total up front and at 30" BOP to throat and I had built out the shelf 3/16". The bow is only 58# @ 29". I had to drop down to 200gr (300 total) tip to get them to fly straight.
I switched to the bare shaft planing method that Adcock proports as the best way and it stopped showing too weak.
Which method should i believe. That is abig difference in spine requirements. I can't believe I need .250 spine shafts for this bow.
-
The HH Heavyweight is suppose to have a deflection of ~.205@28". That seems awfully stiff to me. I posted a question on 3 Rivers website...hopefully they can be of assistance.
-
"I am researching a good starting place for developing an EFOC arrow weighing ~780-830 grains for a 60# ACS bow. I'd like to get as much weight up front as possible (obviously.) These bows are extremely efficient. Is the HH heavyweight too heavy for this? My draw length is 28", so I could cut some length off, if needed. Which Hammerhead shaft do you recommend as a starting point? Thanks!"
Johnathan Karch from 3Rivers Archery said:
"I would say if you are looking for EFOC that you should do just fine with the HH heavyweight carbon arrow. The arrow might be a bit stiff, so do not cut too much off at first. The standard HammerHead would be the best option if you were not going heavy point weight, but I would say if you are looking in the 200 gr + range on the front go HH Heavyweight."
-
chopx2 -- I use the planing method to get me close. I frequently end up reminding myself that I can only tune as well as I shoot. Tuning arrows with BH's in relationship to my fletched shaft is ,by far, IMO the only way that I can be confident. On several occassions I thought I had my bareshafting right on and found my BH's grouping up to 4-5"s differnt at twenty. Slight tweaks to my set-up brought the BH's and fletched shafts together. I have then shot the bareshaft, fletched shaft and the shaft with the BH and all three were w/i 2"s at 20 yards.
-
Friend, Thanks. It was perplexing to me because another bow I had with nearly identical specs acted "normal".
Andy, the key to FOC is putting as much up front relative to how much you have in the back. It is far easier to achieve ultra extreme FOC with lighter weight but stiff spine shafts.
I am not familiar with the Hammerheads, but from what I've read they are heavy which would could drive up total weight very high if you are trying to get over 30% FOC.
slivrslingr - you could shorten the arrow (confirm first with lower point weight before cutting) or you could build out your side plate which will make the arrow act stiffer.
-
Part of the Hammerhead's weight comes from the footing they put up front, but I don't know how much is there. Looks like I'll hafta ask Jonathan Karch @ 3 Rivers...will post when question answered.
-
I'm having an experience a little different from Andy's I'm finding I"m able to tune a shaft that according to all the charts should be astronomically weak. I'm shooting a 58 @ 28 centaur. Im only pulling about 25.5 inches and am shooting a 25.75" beman mfx trad, cut to 25.75 with a 100 grain insert, 300 grain head, cut down wrap and 3 3.5" low profile banana cuts. FOC measures out to 28.6%. Everything I know about arrow selection says this should be way weak. Wrong. It flies like a dart. Bare shafts, fletched shafts and broadheads all fly together out to 25 yards. I'm not complaining just wondering if the effects of EFOC and UEFOC go beyond penetration considerations and perhaps may force us to re-think the effects of foc on dynamic spine reactions. Thoughts?
-
How close to center is your shelf cut? If I understand correctly, the further away from center a bow is cut, the weaker spine it needs so the arrow can progress properly through its paradox. Maybe someone who knows more than I can help!!!???? (shouldn't be too hard to find a gaggle of folks who know more than I know!! :D )
-
Well, scratch that idea. I just looked on Centaur's website, and they cut to center. Hmmm....do you have a built up strike plate?
-
I got a little moleskin on it but even that is shaved down to a bare minimum. Not complaining now, I've got a 29% FOC arrow weighing just above the heavy bone threshold at 670 grains and it flies like a champ. Nope, not complaining, just don't quite understand it.
-
AKCrazyhorse, You are pulling around 46-47.5# at your draw, and the short arrow length probably would just spine right for you.What size mfx are you shooting btw?With a 25.5 draw and 25.75" arrow,doesnt the broadhead touch your finger at full draw with just 1/4" clearance from the back of the riser?I sure would like to ba able to hunt out there in alaska someday,dont know if I can handle the cold though. :bigsmyl:
-
I hadn't considered the arrow length...the shorter ya cut 'em, the stiffer they get.