Isn't a 650 grain arrow a "650 grain arrow"?

[Richie Nell]

So to restate what I thought from the beginning...  
10gpp or any other # of grains per lb. of draw is hogwash when speaking of efficient penetration.  It is only a romantic aspect of arrow trajectory and flight beauty, which is only a few nothces above hogwash.

I understand. thanks

[Rob DiStefano]

Originally posted by Richie Nell:
So to restate what I thought from the beginning...  
10gpp or any other # of grains per lb. of draw is hogwash when speaking of efficient penetration.  It is only a romantic aspect of arrow trajectory and flight beauty, which is only a few nothces above hogwash.

I understand. thanks

I don't think anyone on this thread posted what ya just typed above.  

I can only reiterate/paraphrase what I said b4 ...

Aside from using an efficient and sharp broadhead, mounted on an arra of sufficient spine with good flight characteristics from yer bow with you shooting, I think it's wise to launch as heavy an arra as possible with consideration of the game yer hunting and the average shot distance.

Too heavy and arra for a given bow holding draw weight will reduce arra speed and limit yer effective shot range.  Choose wisely and within yer physical limits.
   
YMMV, but it shouldn't.

[Richie Nell]

Diamond Paul,
"Unless you are hunting elk, moose, or African animals, a well-matched arrow with sharp head is going to give you plenty of penetration."

I agree...I personally am well aware of what it takes to get good penetration on an animal.  HEAVY AND FAST.  That is all me.  That is not my concern personally.
My concern is the recommended arrow setup for penetration that is circulating is flawed.
Especially because SO MANY hunters seem to be using as little bow weight they can get by with.
And if any # of grains per draw weight is  recommended it is wrong.  

Maybe there could be an accurate formula devised for calculating a better RECOMMENDED bow/arrow setup for penetration (aside from broadheads  and flight issues).  Something that would result in....
The decrease in bow strength being directly correlated with the increase in arrow mass to a point.  That point being the flat line of the curve or the bone busting threshhold.  Then the arrow mass would stay stable as the bow weight increases.

I am just thinking on paper now.   :confused:

I know I need more to do but I am waiting on a land closing so I can take off for turkey season.

Sorry guys.      

[Richie Nell]

Rob...that quote is what I am saying not anyone else specifically.  That is exactly what I think for any bow with less strength than about 60 lbs.

[James Wrenn]

Where did the 650gn number come from? Why is that the magic number?You sure would not like shooting a 650gn arrow from one of my 40lb bows unless you were shooting fish.  :D  There has to be some point where you draw the line on arrow weight so you can shoot beyond spitting distance.A heavy arrow that you can't hit anything with it more useless than a light weight arrow you can hit your mark with.There is much more to penitration than arrow weight.It is a combination of proper flight,proper shot placement and a good choice in broadheads.Numbers are great to talk about on the internet but the longer you kill things with arrows the less importance you will see in them.     jmho

[Bill Carlsen]

My wife shoots a 45# DAS bow and 500 grain arrows. I make her arrows, as well as my own, with about 200-225 grains FOC. For both of us we have experienced pass thrus on the deer and bear we hunt. I believe that when it comes to designing a hunting arrow it is important to use high FOC, especially if the arrow, like my wife's, are going to be on the light side. I am sure that if her 500 grain arrows were made using weight tubes instead of heavy heads her heavy headed arrows will out penetrate the same arrow with the weight tubes. Bob Morrison has worked with heavy FOC arrows for a number of years now and his findings were that the heavy FOC out penetrated the same weight arrows without the FOC factor. I guess what I am trying to say is that the total arrow weight is not the only factor....it has to do with where the weight is,  with weight up front being desireable.

[Rob DiStefano]

Originally posted by Richie Nell:
Rob...that quote is what I am saying not anyone else specifically.  That is exactly what I think for any bow with less strength than about 60 lbs.

Please help me understand what yer trying to say, 'cause I'm just clueless at this point.

[DesertDude]

I'm going to take a guess at what he's thinking. If your shooting a 50# bow and your arrow weights 550gr, that's a good arrow set up (11gr pp). Now you shoot that same arrow weight out of a 65# bow and now it's to light. 550gr is 550gr..

I hope I'm on the right track......

[fyrfyter43]

I think the 10 grain per lb. recommendation has more to do with the longevity of the bow than it is a recommendation for maximum penetration.

A lighter arrow will use the bow's energy less efficiently. But that energy has to be absorbed somewhere...namely the bow. That's why a bow will be noisier with a lighter arrow, and a heavier arrow will do alot to quiet a bow down.

My Turkey Creek is a little noisy with the 580 grain (11.6 gpp) GTs I just tuned for it, but was whisper-quiet with the 730 grain (14.6 gpp) ash arrows I tried. Of course, the heavy ash arrows had the trajectory of a sash weight out past about 15 yards.

I'm sure that the extra energy being absorbed by the bow has got to have some long-term affect on the bow, just like using a FF string on a bow without the nocks being built to handle it. But are we talking about 20 arrows? 100 arrows? Thousands of arrows?

Doug (from Turkey Creek) has a disclaimer on his warranty that states "Use of arrows weighing less than eight grains per pound of draw weight
can damage your bow and will void your warranty." I'm sure most other bowyers have a similar disclaimer in their warranty.

[Terry Green]

Richie...I get what you are saying, and it IS hard to convey...I've tried it here many time with failure.

A 650 grain arrow IS a 650 grain arrow, and it has a certain amount of energy depending on the speed it travels......the bow is OUT of the equation when the arrow is in flight.

A 650grain arrow going 175 FPS  has an 'amount of energy' and the poundage of the bow is irrelevant as far as that 'amount of energy' is concerned.  The 650 grain arrow reached 175, but it has no clue what bow got it there, but it still has the 'amount of energy'.

I think what Richie is saying IS......

We should be looking at the arrow weights and speeds for TRUE data of the power an arrow has, and the '10 grains per pound' is not as accurate as a measurment.

45# bow and a 450 grain arrow at 175 FPS - OK

Same bow model at 65# with a 650 grain arrow at 175 FPS - OK

Same 10 grains per pound but NOT the same penetraiting energy...not even close.

Again, I think Richie is trying to seek more accurate arrow weight and speed data for penetration to achieve what he needs, and by measuring arrow wieght and speed he's going to come much closer to true data than just going by the 10 grains per pound.

I hope that made sense, cause I've run this horse through here several times before with no luck.

[Bjorn]

Personally I shoot about 12-13 GPP; but somebody please tell me about the empirical evidence any bowyer would use to discern if you have been shooting 7 GPP or 9 GPP.

[Dr. Ed Ashby]

Below is an excerpt from the Part 4 Update. Hopefully, it will help clear up the meaning of the threshold.

******************

"NOTE: Some folks seem to misinterpret the "Heavy Bone Threshold" to mean that only arrows of this mass or greater ever penetrate heavy bone, or that any arrow above this mass always penetrates heavy bone. This is incorrect.

The Heavy Bone Threshold is merely a point of arrow mass where the data indicates an abrupt and marked increase in the frequency of heavy bone penetration. It is present for all broadheads tested, of all types, and is consistently near a mass of 650 grains; ranging from approximately 625 grains for the high MA single-bevel broadheads, to approximately 675 grains for some low MA broadheads.

Above 'threshold value' the probability of heavy bone penetration abruptly increases for all broadheads tested. However, the increased frequency is not equal in either degree or amount for all broadheads. Some jump from virtually zero to 10 or 12 percent, while other might jump from 20 or 30 percent to 65 or 70 percent. In all but extremely massive heavy bone, and when arrow-integrity remains intact, the best overall-design broadheads show frequency jumps from ­85 or 90 percent to a full 100% frequency. Broadhead type, bevel type, tip type, main blade profile, broadhead MA and ferrule profile are all strong influencing factors.

For fresh in situ bone, the Heavy Bone Threshold is a definite and persistent, thoroughly repeatable entity. Testing into both 'old bone' and extricated fresh bone proved equivocal, showing poor correlation to in situ results. It is suspected that changes in composition influences 'old bone' results, and absence of supple support from cushioning collateral tissues influences extricated-bone results. Irrespective or cause, these media do not yield outcomes consistent with that shown by fresh, in situ bone.

For a given broadhead, the Heavy Bone Threshold shows little change throughout a fairly wide range of impact forces. It is theorized that this is because the Heavy Bone Threshold represents a time of impulse which acts ('pushes') sufficiently long (time wise) to exceed the structural limits of a heavy bone's supporting matrix; more so than the level of 'raw force' applied. A loose analogy might be: how an armor piercing round applies the impact force it carries is far more important in penetrating a tank's armor than is the level of raw force it carries."

******************

Some recent testing on several fairly fresh-kill (but somewhat more than 30 minute limit usually employed) Georgia whitetails, conducted by Wesley Mulkey with a couple of those 'C-bows' and a series of arrows from 450 to 777 grains, stringly suggest that the threshold persist for whitetail heavy bones too; the head of the humerus/scapula, scapular ridge, hip joints, pelvic girdle and vertebral bones (as opposed to the spinal joints) - even at the very high impact force levels he employed in these test. A 'fresh set' of in situ bones was used for each shot, so 'prior damage' did not affect outcomes. The threshold level appears approximately the same as that shown by buffalo ribs; somewhere between 625 and 675 grains. Hopefully he will collect more such data next year.

For  the same BH and like arrow setups, at HIGHLY DIFFERENT impact force levels the 'baseline' penetration rate for a given BH might be SOMEWHAT different below the heavy bone threshold, BUT ONLY MODESTLY; far less than most would expect. Despite their slight difference in 'baseline' penetration rates, at the heavy bone threshold of arrow mass A SIZABLE and ABRUPT INCREASE in the rate of heavy bone penetration is manifest for each.

Having arrow mass above threshold does not guarantee heavy bone penetration. Lots of variables effect the final penetration rate. However, for all broadheads, your ODDS of penetrating on a heavy bone impact gets FAR better when mass is above the heavy bone threshold; for the BH you use. It's there for arrows traveling 119 fps, and those traveling way over 200 fps.

Hope that helps clarify,

Ed
TGMM Family of the Bow

[Richie Nell]

I think that clears up why any # of grains per lb. of draw has NOTHING to do with penetration.

It is a specific grain arrow at a specific speed (aside from broadhead and arrow flight)

[JC]

Originally posted by Richie Nell:
I think that clears up why any # of grains per lb. of draw has NOTHING to do with penetration.

No, not for bows above 65# if you go by the 10gr/# rule....

Yes, I would agree with Doc's hypothesis that the threshold weight is 650gr...he's got too much data for me to argue with in that regard.

But, for me, I don't choose my arrows solely on how well they penetrate...a major factor yes, but not the exclusive one. I typically shoot arrows in the 550-600gr range out of my lighter (57-59#) bows because I like the trajectory afforded of those weighted arrows out of bows of those weights. And, just for me again here, increasing the odds of hitting the spot I want (by improving trajectory and therefore improving vertical margin for error) on thin skinned game,  is worth the potential tradeoff of slightly decreased penetration by losing 50-100gr.

With my heavier bows (63-70#), 600gr+ is the norm, but again, only because I like to balance my preferred trajectory with arrow mass.

Out of all of my bows (lowest 57, highest 70), I have found 9.4-9.8gr/# to give me that best compromise. Now, all of these are typically 12-20% foc, so that fact cannot be overlooked: To date, with Trad gear, using this gr/# and high foc rule of thumb, I have yet to have a complete passthrough on an arrow that hit a big game animal. Purely anecdotal but until that stops happening, I'll keep using it on the animals I hunt. Your mileage may vary...

Hook me up with an Aussie buff hunt Doc and I'm sure you can totally convert me to your thresh hold weight    

[DesertDude]

That's interesting JC.  When I got my Brackenbury Quest this year, I called Bill to ask him a few questions. He inreturn asked me what weight arrows I would be shooting out of it (57#@28") I responded with 10Gr per pound, He informed me that with his testing results, 9.2gr to 9.6gr is what performed best. Very close to your results.

[Richie Nell]

Desert...

"He informed me that with his testing results, 9.2gr to 9.6gr is what performed best."

What did he mean by "performed"?

richie

[Richie Nell]

JC..you say not for bows above 65#s.  
Bows above 65# should be fine.  That is 650+ grains.
Don't you mean NO to bows less than 65#s?

Ex.  45 lbs shooting 450 grain arrows.  

TOO LIGHT

[Diamond Paul]

I assume that 650 grain number to coming from Dr. Ashby.  I think he might argue that a 650 grain arrow from a 45lb bow might penetrate better than a 450 grain arrow from same bow, even though it would be flying at a slower speed.  Probably true.  But a 450 grainer (10gpp) will have a more useful trajectory, will absorb enough bow energy to be pretty quiet, and will penetrate sufficiently on the type of game 45lb bows are typically used for.  Once the head comes out the off side, additional penetration is not a necessity.

[Rob DiStefano]

Well said, JC.  

For me, it's all a compromise of arra weight and arra speed, balanced by keeping the GPP no lower than 9 and using at least 20% FOC.  

I want an arra that exhibits a minimal 15-30 yard trajectory compromise.

[Molson]

Considering 10gr per pound of bow weight a heavy hunting arrow, while paying no attention to what the actual weight is, is nothing more than socialism for bowhunters.

Set up being identical, a 400 grain arrow from a 40 pound bow will never equal the killing power of a 600 grain arrow from a 60 bow.  Never... not at any range.

I do not understand "useful trajectory" as it pertains to hunting.  My son has a 40# longbow which will happily shoot 600+ grain arrows all day long at 25 yds.  It takes perhaps 5 shots to adjust to this bow at that range.  At 15 yds, his maximum hunting range, there is no difference in trajectory and no meaningful difference in speed compared to a 420 grain arrow.  There is a huge difference in how hard they hit.

Extending range by lowering arrow weight does not equate to effectiveness in the field.  It seems to me, the exact opposite is true when using lighter weight bows.