Trad Gang
Main Boards => Dangerous Game => Topic started by: eugeneb on March 25, 2010, 03:11:00 AM
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Hi,
The speed vs weight concept relating to penetration fascinates me. (bowhunting) I have read numerous articles of people professing KE vs Momentum to be the best indicator for penetration. I have read Dr. Ashby's research with great appreciation and I lean towards the momentum formula ... nevertheless, using either KE or Momentum as an indicator for best penetration ... results in using the combination of velocity and weight (mass) of an arrow. I see many people saying heavier is always better? (I will use my new compound as an example to bring across my question/point)
I have ordered a new compound bow (not yet received and did some planning so long) ... I will use it as an example, the way I figure the best penetration specific to the bow ... taking into account each bow's effiency will differ (i.e. power stroke and how the bow transfers energy to the arrow) Surely the same logic should apply to trad bows in determining the best momentum, which seems to be the best indicator for penetration.
The new bow specs as follow: IBO=330fps, #70 dw, 32" dl, 5 grain on string ... I have used 2 different arrow speed calculators to estimate the arrow speed at various arrow weighs (total arrow weight) ... took the average speed and calculated the KE and momentum ... this obviously is not the real world, but gives me an indication (range) where my bow will perform optimum for example around penetration (momentum)
My question is ... whether heavier always better? For me it is striking the balance between velocity and weight ... e.g. according to the momentum formula my penetration is better with a 700 grain arrow opposed to 1000 grain (obviously all else being equal ... broadhead mech advantage, shaft diameter, eFOC, etc.)
I would appreciate your comments on whether these assumptions are correct. I have included some figures as example.
(Reason for my question is that I plan to hunt Aus Buff and would appreciate to understand whether momentum is a better indicator than purely using a heavier arrow)
(http://i901.photobucket.com/albums/ac217/eugeneb_photos/KEMomentumChart.jpg) (http://s901.photobucket.com/albums/ac217/eugeneb_photos/?action=view¤t=KEMomentumChart.jpg)
Momentum below
(http://i901.photobucket.com/albums/ac217/eugeneb_photos/MomentumGraph.jpg) (http://s901.photobucket.com/albums/ac217/eugeneb_photos/?action=view¤t=MomentumGraph.jpg)
KE
(http://i901.photobucket.com/albums/ac217/eugeneb_photos/KEGraph.jpg) (http://s901.photobucket.com/albums/ac217/eugeneb_photos/?action=view¤t=KEGraph.jpg)
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all of the above charts show formulas and projected energy, but if you want to know what will really happen then test it. i did this for my sons science project recently, showing 300, 400, and 500 grain arrows of similar construction, from a wheel bow to a consistent draw, from a set distance. we measured penetration, avged 10 shots from each group, and heavier won.
you have to apply intent into the equation as another variable that you must interpolate intrinsically, meaning...we all know that the extremes on both ends of the above projected resultant energy charts are not useful hunting applications (example when the 220 Swift first came out, some idiot publisher touted that it was so fast and produced so much KE from speed that you could hunt lion with it...i'd like to see that...also on the opposite end of the spectrum pure weight alone won't do it either)
so analyze for intent...you must hit the animal, which is aided by speed and its affect on trajectory, and once that is accomplished you want the benefit of weight.
maybe i just oversimplify things...but i have never seen the point in this argument...shoot the heaviest arrow that you can that allows you to fall within a viable spectrum of velocity (and if the result is not acceptable then you must change the platform, ie increase pull weight, etc). if possible actually test and manipulate both variable to optimize both...there is an optimum in the middle somewhere
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KE decreases with increasing arrow weight?
http://www.huntersfriend.com/carbon_arrows/hunting_arrows_selection_guide_chapter_5.htm
Above according to a chrono. Have been told that many of the online programmes using IBO speeds have significant issues;-] especially with heavier arrows.
If my info is incorrect, apologies in advance.
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If your new bow actually will spit a 700 grain shaft at 230 plus then there is little further thought needed, or I would think so anyway. To help answer your question a bit as to the reduced momentum with heavier shafts, well all tools eventually reach a point of diminishing returns and sporty new compounds are no exception. Actual testing will be much more revealing however, as any bow's efficiency will generally go up with increased arrow weight.
When I am able to put my long bows away (not common)I shoot a speedy 70# compound as well, using 620 grain shafts with 24% FOC. And they are penetrating 15" into one very tough crossbow target. Or just a scant inch or two more than my 80# longbow with 770 grain shafts.
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Hi,
Thanks 4 all the info ... I actually posted the same question on another forum and someone also pointed out that the speed calculators are inaccurate on heavier arrows ... his bow is simular to mine (eg: 400gr arrow the same as my example) ... but he indicated his bow spits out a +1000gr at 214fps ... he actually inserted his setup into the same speed calculators I used with the result being 147fps ... as stated do not rely on speed calculators for heavier arrows ... perform actual tests yourself ... in essence this changes every for me, my best penetration seems to be way more than 700gr ... again thanks for your posts ... I will wait for my bow to check out actuals. (in other words the figures posted relating to the heavier arrows is way off the mark)
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looks to mee that the wheel bow doesnt tranfer energy to a heavy arow very well
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My pet peeve for 3 years has been the same computer whiz kids that gave us "toxic tranche mortgage bundling guaranteed not to fail" software also devised Bucklemke.
Nothing wrong with wheelie compounds, eugeneb used a worthless programme that also fails in the real world.
jrchambers, click on my link then compare with a recurve test from www.bowreports.com (http://www.bowreports.com)
Energy in energy out add in momentum, Ashby and voila a passsionate debate. thanks
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As fentiger said ... I used a worthless application (actually two of them) to calc the speeds ... it seems the speed calcs are fairly accurate at the lower arrow weights ... big difference between 214fps (real world) and 147fps (speed calc) on 1000 grain arrow ... I'll reserve my comment untill I have checked it out myself = lesson learnt! ;-)
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Why here? Are there really no 'compound bow sites' for you to have these discussions?
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Originally posted by Bjorn:
Why here? Are there really no 'compound bow sites' for you to have these discussions?
he won't get near the quality answers from them as he will get truth here.
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Bjorn, I wondered the same thing. It must be because Dr. Ashby was invoked early on.
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Hi Guys,
I was contemplating whether I should answer.
Grapes is 100% correct in his comment. Further my intention is not to discuss/promote wheelie bows, rather my interest and the topic objectives was to gather info around penetration and the related attributes.
More and more compound forums makes reference to Dr Ashby's reports and refer to the tradgang site ... and in my opinion, through his fascinating research is changing the views of compound archers (for the better) and more compound archers are going heavier arrows and two-bladed bh's. Which I think is a good thing for archery in general and should be a feather-in-the-cap for the trad guys and this site.
As Grapes stated, I have learnt more from this forum in a short space of time than I would have from another ... that is why I chose it ... real world information!
My intention is not to invoke a huge debate around this and if you feel my post is offensive or out of line re Tradgang's policy ... let me know.
Cheers - Eugene
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I think this is as relevant for traditional archers as it is for compound shooters - almost. Traditional bows have a hard time reaching the speeds of a compound bow, therefore we emphasize more on weight than on speed, to maximize the joule. But I too have thought about this matter. I shoot 10GPP arrows, and speed is fairly good. A 700 grain arrow shot from one of my 70# bows should be enough to take out most game, so I'm not worried about that. I find that weight is important, as it maximizes the bows effiency, but I would probably not go heavier than 10GPP, unless I had to kill a buffalo. Versus quicker reacting game, I believe that speed is just as important.
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Thanks Fatboy ... what made it more relevant for me was to understand whether my #70 can take a buff or whether it would be too light; and also ensuring I am not too light in the arrow department. Lots of contradicting info on the WEB ranging from 550-1000 grain arrows, and professing draw weights minimum #80
I got all the info I required from this forum (thanks) and also met up with Ozy Clint
I selected the following:
- Easton FMJ DG (thin diameter) arrow;
- 75gr brass insert;
- German Kinetic bh 210grain;
- total arrow weight 850 grain @ 219fps.
(havn't checked my FOC yet)
Hopefully I can crack a buff rib with this and not return via the newspaper.
Thanks
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fentirger.
Yes, KE decreases with increased arrow weight out of the same bow. The KE has velocity squared as a factor which pumps up the numbers based on velocity. Increased arrow weight out of the same bow means decreased velocity = decreased KE.
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So according to the calculator on the link above, my 68# longbow throwing a 547 gr arrow at 168 fps is barely adequate to drop a whitetail deer. At 34.3 ft lbs I have a better chance of injuring myself then a black bear and yet I know this is not true. I think physicist don't hunt!!!
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Originally posted by Northwest_Bowhunter:
So according to the calculator on the link above, my 68# longbow throwing a 547 gr arrow at 168 fps is barely adequate to drop a whitetail deer. At 34.3 ft lbs I have a better chance of injuring myself then a black bear and yet I know this is not true. I think physicist don't hunt!!!
I did the math a few years ago on my hill bow, and laminated birch arrows, and was right around 30 ft lbs, and the deer tasted good. I do believe it is all about placement. Yes higher odds will increase your numbers, but if the placement is bad, so is everything else.
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Originally posted by Ragnarok Forge:
fentirger.
Yes, KE decreases with increased arrow weight out of the same bow. The KE has velocity squared as a factor which pumps up the numbers based on velocity. Increased arrow weight out of the same bow means decreased velocity = decreased KE.
I have always been a firm believer that speed kills, but mass destroys. You could throw a brick, and yes it would hurt, but throw a bowling ball, and it will destroy it's target. Yes it will be slower, but much more deadly.
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I think a compound shooter made that chart, native Americans were killing buffalo long before they could achieve those speeds.
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I am still a little confused by all of this KE momentum debate. I know for a long time other hunters and myself have had great success with 45#-55# bows shooting arrows between 450- 600 grains with a good broadhead. I have had complete pass through shots on deer with arrows as light as 485 grains from a 50# and 55# longbow with good old zwickey 2 blades. I have never shot a arrow over 560 grains for deer or hogs and never had a issue. Plains indians were taking buffalo with 35# bows and stone heads I think we have a pretty good chance with what we have today. Just my 2 cents worth.
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If we were trying to penetrate animals with blunts, the energy figures would be very pertinent. With a cut-to-tip broadhead, arrow stability and broadhead sharpness become the more important factors.
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If you read the Ashby articles on here you will see that KINETIC energy DOES NOT PREDICT penetration. And the complete physics analysis proves it.
What the compound shooters and the industry that supports them has done is create a myth to sell product.
Speed will only increase penetration if mass (arrow weight) stays the same. This results in a momentum increase (speed is not squared). Of course you must keep perfect flight the same. Weight does not change at impact, but speed decreases rapidly. So the more momentum is made up of in speed the less it will penetrate because retained energy is much less than the the same impact momentum achieved through higher weight and less speed.
Using the bowling ball example. Throwing the bowling ball harder will cause more damage assuming identical impact angle and placement. Dropping down to a softball so it will go faster actually reduces the damage. That is where fact gets confused with fiction.
Hope that makes sense when you read it...lol
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i have never understood KE nonsence when talking about archery equipment.
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sounds like you are ready to go eugene. now comes the hard part....getting access to buffulo. i wish i could have helped you out. good luck.
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ditto !!! to you Ragnarok Forge……. :thumbsup: :thumbsup:
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AND ditto to You too GRAPES !!!!!! :thumbsup: :thumbsup: :notworthy: :notworthy:
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Originally posted by Ragnarok Forge:
fentirger.
Yes, KE decreases with increased arrow weight out of the same bow. The KE has velocity squared as a factor which pumps up the numbers based on velocity. Increased arrow weight out of the same bow means decreased velocity = decreased KE.
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grains 450
speed 220
KE 48.35164835
Momentum 0.43956044
grains 500
speed 200
KE 44.4000444
Momentum 0.444000444
grains 550
speed 180
KE 39.56043956
Momentum 0.43956044
grains 600
speed 160
KE 34.0992341
Momentum 0.426240426
I don't consider KE in anything I do as it to me is irrelevent. KE might get the arrow to the hide, but it is momentum that will finish the job.
The point of this illustration, is that the last value, 600 grain arrow at 160 is exceeded by my 45# Dorado, which some say is more like 50, or at my 31" more like maybe 55-60 some say... but the point is, but anyone here will attest to the fact that there is little out there that will not drop to this formula.
Just as an aside, I've been using 700 grain arrows and get 170 fps minimum from the Dorado with them and result goes up from what we have here.
Point of all of this, is momentum carries the arrow, and reduced speeds is no penalty.
grains 700
speed 170
KE 44.91064491
Momentum 0.528360528
Much Aloha... :cool:
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Rattus58, from which bow did you get those numbers?
I don't know why so many archers still believe that joke "KE is decreasing with arrow weight"
Ragnarok, your assessment is absolutely wrong.
From most of bows, traditional AND compounds, from same bow shot at the same drawlenght with same release, both KE and Momentum will increase. BECAUSE DYNAMIC EFFICIENCY OF THE BOW INCREASE WITH ARROW WEIGHT. Past 13 to 15gpp according to the bow design, that increase will indeed be minor but still significant.
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Hi Hybrid... the only number that is mine is the last one, 700 grains with a 45# Dorado... People tell me that the Dorado could be heavier but I don't know. I have a 31" draw, so it's subjective, but I do have a chrony that is consistent in readings so this is what I use when I shoot...
That said.... KE has to go up with an arrow weight given the ratio of weight to speed.
Weight can provide a diminishing return but speed has to reduce fairly dramatically along with weight increase being small.
grains 450
speed 220
KE 48.35164835
Momentum 0.43956044
grains 500
speed 200
KE 44.4000444
Momentum 0.444000444
grains 500
speed 180
KE 35.96403596
Momentum 0.3996004
Much Aloha... :cool:
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Might add, momentum again is the driver of the arrow in game, KE gets it there but become irrelevant once the points hits the hide.
Aloha... :cool:
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This is interesting stuff, physics has always been a little difficult for me, but this helps. That being said, sharp broadheads, perfectly tuned arrows, and proper shot placement kills game, not math.
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Precisely.....
Aloha... :cool:
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i tested extensively my bows in order to determine realistic performance measure before my trip to South africa and... for the fun of archery too ! :
i was shooting seated on the rinehart target my four hybrid bows with 4 arrows through a chrono with a checked draw length @ 31" BUT the shot was done to hit the "vitals" of the target # 11 yrds and valid only if so.
All arrows were tuned rather good for the shot distance with each bow (of course not "perfect" with all...) and were really made to hunt with high penetrating power with point weight (insert+BH) ranging from 280 gr to 325 gr
(http://i758.photobucket.com/albums/xx225/hybridbowhunter/DSC027501-560x1024.jpg)
(http://i758.photobucket.com/albums/xx225/hybridbowhunter/DSC027531-1.jpg)
(http://i758.photobucket.com/albums/xx225/hybridbowhunter/DSC02779.jpg)
(http://i758.photobucket.com/albums/xx225/hybridbowhunter/DSC02774-1024x768.jpg)
Those are the numbers, and as you see, with no exception from the same bow/archer KE increase with arrow weight (and of course momentum)
Guys, when you shoot a bow, if you make well tuned arrows, there is no way you loose "work" of the arrow when increasing the weight
Morrisson (61,1 # @ 31) :
878 gr (14,37 gpp) / 162 fps/ KE 51,2
735 gr (12,02 gpp) / 175 fps/ KE 49,99
682 gr (11,16 gpp) / 178 fps/ KE 47,99
619 gr (10,13 gpp) / 186 fps/ KE 47,56
Fedora (62, 8 # @ 31):
878 gr (13,98 gpp) / 165 fps/ KE 53,09
735 gr (11,70 gpp) / 179 fps/ KE 52,31
682 gr (10,86 gpp) / 184 fps/ KE 51,28
619 gr (9,86 gpp) / 190 fps/ KE 49,63
Fedora (56,9# @ 31):
878 gr (15,46 gpp) / 161 fps/ KE 50,55
735 gr (12,94 gpp) / 173 fps/ KE 48,85
682 gr (12,00 gpp) / 178 fps/ KE 47,99
619 gr (10,90 gpp) / 185 fps/ KE 47,05
Cari Bow (59,4 @ à 31):
878 gr (14,78 gpp ) / 161 fps/ KE 50,55
735 gr (12,37 gpp) / 174 fps/ KE 49,42
682 gr (11,48 gpp) / 180 fps/ KE 49,08
619 gr (10,42 gpp) / 188 fps/ KE 48,59
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Finally for my african trip i took my Fedora 57# and my cari bow 59# and made a 675 grain arrow (with 320 gr up front) flying perfectly for me up to 30 yards with the BH.
And that worked quite ok if you wanna look there: http://tradgang.com/noncgi/ultimatebb.php?ubb=get_topic;f=27;t=000317
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Did you consider hunting the buffalo?
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I wish to hunt buffalo ! and hopefully i will do it in a couple of years but not in South Africa as my will for buffalo is a more free range hunt.
My set up for that hunt would be the Fedora 63# and the 735 gr arrow with 325 gr in front which indeed was the "perfect" arrow for that bow & set of limbs. and would switch from 3 blades large broadheads to 2 blades standard width.
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Originally posted by hybridbow hunter:
i tested extensively my bows in order to determine realistic performance measure before my trip to South africa and... for the fun of archery too ! :
i was shooting seated on the rinehart target my four hybrid bows with 4 arrows through a chrono with a checked draw length @ 31" BUT the shot was done to hit the "vitals" of the target # 11 yrds and valid only if so.
All arrows were tuned rather good for the shot distance with each bow (of course not "perfect" with all...) and were really made to hunt with high penetrating power with point weight (inert+BH) ranging from 280 gr to 325 gr
(http://i758.photobucket.com/albums/xx225/hybridbowhunter/DSC027501-560x1024.jpg)
(http://i758.photobucket.com/albums/xx225/hybridbowhunter/DSC027531-1.jpg)
(http://i758.photobucket.com/albums/xx225/hybridbowhunter/DSC02779.jpg)
(http://i758.photobucket.com/albums/xx225/hybridbowhunter/DSC02774-1024x768.jpg)
Those are the numbers, and as you see, with no exception from the same bow/archer KE increase with arrow weight (and of course momenum)
Guys, when you shoot a bow, if you make well tuned arrows, there is no way you loose "work" of the arrow when increasing the weight
Morrisson (61,1 # @ 31) :
878 gr (14,37 gpp) / 162 fps/ KE 51,2
735 gr (12,02 gpp) / 175 fps/ KE 49,99
682 gr (11,16 gpp) / 178 fps/ KE 47,99
619 gr (10,13 gpp) / 186 fps/ KE 47,56
Fedora (62, 8 # @ 31):
878 gr (13,98 gpp) / 165 fps/ KE 53,09
735 gr (11,70 gpp) / 179 fps/ KE 52,31
682 gr (10,86 gpp) / 184 fps/ KE 51,28
619 gr (9,86 gpp) / 190 fps/ KE 49,63
Fedora (56,9# @ 31):
878 gr (15,46 gpp) / 161 fps/ KE 50,55
735 gr (12,94 gpp) / 173 fps/ KE 48,85
682 gr (12,00 gpp) / 178 fps/ KE 47,99
619 gr (10,90 gpp) / 185 fps/ KE 47,05
Cari Bow (59,4 @ à 31):
878 gr (14,78 gpp ) / 161 fps/ KE 50,55
735 gr (12,37 gpp) / 174 fps/ KE 49,42
682 gr (11,48 gpp) / 180 fps/ KE 49,08
619 gr (10,42 gpp) / 188 fps/ KE 48,59
Beautiful Bows... :)
Aloha... :cool:
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I spent 2 summers shooting my osage orange recurve through a chronograph from 10 yards out to 40 yards. All arrows were woodies of different species ranging from POC to Hickory. All arrows were spined properly and all arrows flew very well. I was mostly testing to see if the different tapers on a shaft made any difference in velocity at hunting ranges. They do not. The arrow speed at 40 yards is the same no matter how the shaft is tapered. All arrows with in 10 grains of each other shot the same speed no matter the taper or the wood. I suspect that a barrel tapered shaft shot a bit further at 400 yards than a straight tapered shaft. If it didn't then the armies of old wouldn't have gone to the expense to barrel taper shafts. When I put the E=MCsquared conversion formula to the grain weight of arrows, my self bows were most efficient at 11 grains per pound of bow weight. I.E., a 65# bow shot most efficiently with a 714 grain arrow.
With out a heck of alot of balistic jelli i think this is the best method of determening what shaft to shoot.
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good read.
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Hybrid Bowhunter,I pay little attention to KE figures normally and believe momentum is more relevent.During a similar discussion however,I went back and used my actual chronoed speeds etc to calculate KE to see if it actually dropped as arrow weight was increased.
I found exactly as you did.KE increased with increases in arrow weight.With access to a chrony,anyone can figure that out very quickly.I still find the momentum figure seems to be a better predictor of how penetration increases when arrow weight increases.
Rattus 58,the speeds you list with changes in arrow weight are way off.When I chronoed different arrow weights out of 50-55# bows,it took almost 100 grs of arrow weight to change speed 10fps.You are showing 20 fps loss when adding 50 grs of arrow weight.It can't happen.It would be more like 5-6 fps loss in real life.I assume that is why your KE numbers are off.The speeds just aren't real.
The arrow weights I tested were 10-14 GPP.
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this just keeps getting better with info, thanks
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proper shot placement is the key to your success . shoot a 500 plus grain arrow and put it in the pump station. leave all math to mathematicians
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Some African countries have KE recommendations for different classes of game.According to those KE charts,our bows are only suitable for jack rabbit sized game.This,despite the fact that traditional hunters go over there every year and blow clean through the largest species of plains game with bows that the KE chats say are inadequate.Now when you run the momentum figures,these bows compare much more favorably,mostly because of the weight arrows we shoot.
If you haven't read it already,this is a very well written article on the subject.
http://www.africanarcher.com/momentumKENETICS.html
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KE is the measure of energy stored in the arrow during flight. Momentum describes how the energy is released on impact. KE is entirely irrelevant to penetration. The laws of physics have not changed. A 700 grain arrow travelling 213 fps will kill a rhino. You have plenty of weight and speed.
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I have done extensive testing on numerous occasions starting roughly 25 years ago……I have tested using both recurves and compound bows.
It is my opinion that when hunting with a modern compound bow for whitetail size animals, just about ANY combination will work fine for an adult.
It is also my opinion that when using marginal setups(short draw and light draw compounds, or just about any recurve/longbow) that higher momentum is a much better choice for penetration on big game animals.
One thing that is NOT my opinion is that as long as the arrows dynamic spine is acceptable for whatever type of bow you are shooting it from, increased arrow weight ALWAYS equals increased momentum, AND increased kinetic energy. That is just a fact. :)
I have tried to prove the law of physics wrong with literally dozens of bows with widely varying draw weights, shooting dozens of arrow combinations with widely varying total weights. Physics whipped me every time, with no exceptions. LOL