For you heavy arrow guys

[Jesse Peltan]

I was checking out a thread where a guy was wondering about a setup for africa. He was shooting a 70#bow and was not yet set on arrow weight. It turns out that past 1000grains his momentum started to decrease. That means that there would be LESS penetration past 14.5gpp. Now I know this number may change from person to person, but the point is that once your arrow gets so heavy you lose penetration and speed, so if your shooting a 40# bow and 700grain arrows you could very possibly get better penetration and speed at 550-600grain arrows.

[frassettor]

I'm right around 12.5 gpp..I will be watching this one.

[Jesse Peltan]

12.5 gpp should be right around the point of diminishing returns for max penetration. Basicly if you have a bell curve your at the max penetration end(right before the drop off) of the bell.

[frassettor]

how did you figure that out, or was it  other other post you were reading?:

[Jesse Peltan]

12.5 is just under 14.5 so your should be around the point of diminishing returns.

[Jesse Peltan]

I forgot. You won't know for sure until you get chrono #'s for your bow.

[HATCHCHASER]

I read about a study that showed that beyond 12.5 grains per pound is the point of diminishing returns.  I think it was in an issue of TBM.

[Ragnarok Forge]

Heres the problem with studies that claim to cover everything.  

They can't accout for all the factors.

Say I take my 55lb , 68 inch longbow that I draw at 30.5 inches.  I set up a variety of arrows from 11 gpp to 15 gpp and keep the shaft diameters, broad head type, bevel type, the same.  I will have to be adding weight somehow, and the spine of my arrows will be different.  Thus my penetration characteristics of each arrow will change.  

This one is pretty much only quantifiable for one bow and arrow set up at a time.  If you choose one method for adding weight, inserts up front vs weight tubes, etc.... you penetration will also change due to changing foc and arrow paralax recovery.

The good new is there is definately a point of diminishing returns and it can be found thru some serious effort for each bow.

[Jesse Peltan]

The only way to really know is to shoot all the arrow weights into a target and see what penetrates best. 12.5 sound good though as a rough estimate.

[JimB]

You can set up different sets of arrows for the same bow and have them all perfectly tuned to that one bow,meaning,their dynamic spines are the same though you started out using shafts with different STATIC spine.You could make a set of say 2016's,tune them to the bow and make another set of 2018's or 2020's and tune them also with the same broadhead but use a longer shaft(same diameter)and heavier adaptor and insert.These arrows will have same diam.,shaft material and broadheads and same dynamic spine if both are perfectly tuned to the bow.They will weigh differently and have different FOC's.

I did the same thing with a set of 55/75 GT's and another set of 75/95's for the same bow.Same diameter arrows with broadheads out of the same dozen pack.The 75/95's had to be 2" longer and more front end weight(adaptor and insert) so there is more FOC with them.

Dr Ashby often tunes several different weight sets of arrows to one bow to test different weights and FOC's.

[OS]

I've been playing with bows for almost 25 years and have worked in many pro-shops, Heavy arrows offer great penitration but I found over and over again arrow that fell 8.5 to 9.5 grains per inch matched penitration but kept arrow speed up a little bit if you took a shot beyond 25 yards.
I did find that an arrow could get to heavey and decrease penitration at some ranges past 15 - 18 yards.  That 8.5 to 9.5 seam to be the best in penitration, speed, and bow noise reduction. Now I do alot of that at the tip shooting 215 gr Snuffers but have had no problem shooting through deer, bear, turkey or wild hogs

[elkbreath]

It does make sense in the one sense of the argument...Momentum.  

All other things being equal (absurd I know) if one arrow weighs 500 gr and the other 50,000gr, its obvious which will penetrate further since the ultra heavy arrow will likely never leave the bow.  Pair down its weight till it barely leaves the shelf, and it still won't penetrate.  Make it barely get to the target...say 2000grs, and it might just bounce off...  So yes there must be a point of diminishing returns.  Using momentum as your one factor, one could find that point of diminishing returns by chronographing the heaviest arrow they can shoot with perfect flight versus another light one, do the math and there you would have an answer of whether that super heavy shaft would out penetrate, again using only Momentum as your definition.

Ashby felt that it was closer to 14grains per lb I believe.  But again, you can't know it with out speed measurements and math work, and this only deals with momentum, all else being equal.  

A 70# ACS cx is going to be able to efficiently return far more momentum than my snake backed character bow of the same weight at ANY gr per lb.

[JimB]

Ashby has started some testing with a 40# bow and 700 gr arrows that were 35% FOC.He was getting complete penetration and exits 100% of the time on younger bull water buffalos (animals the size of huge bull elk but with thicker skin).

700 grs is 17.5 grs per pound.

[elkbreath]

awesome..gotta get close!

[ozy clint]

i have done a bit of chrono testing in finding out what weight arrow to use out of my 69# recurve on water buffulo. using momentum like elkbreath says as the means to compare each arrow weight, i found, for my bow, that momentum kept increasing with arrow mass until 1000grs at which point momentum went backwards.

i have since settled for a 890gr arrow, which flys great. now i've just got to see a buffulo when i go out hunting.  

[Benny Nganabbarru]

Originally posted by JimB:
He was getting complete penetration and exits 100% of the time on younger bull water buffalos

Impossible on any pig-sized animal and above - a small pig's spine can stop a 1200 grain arrow from a 78# bow, for instance. Unless he hasn't taken many of the shots described above, there is no way "100%" can be be claimed.

[Biggie Hoffman]

This seems like aot of thought for no real reason. At 20 yards a 1000 gr arrow from a 70# bow is gonna give complete penetration.

[swampthing]

Potentially, less and diminishing penetration once weight rises past 14gpp. As your momentum figures go "stale" you may reach a point where you just don't "need" that much more weight. Even with my decent shooting abilities, 11gpp is what I shoot for. It helps my consistancy by absorbing my inconsistancies.
  I would state that a lot would depend on the efficiency of the bow "and" draw length. With an ACS-CX you may find that @14gpp you are still 150fps and with a straightlimb non carbon 150fps may be when you hit 11gpp, with a 28" draw.

[Jesse Peltan]

Were not just talking about a 70# bow with a 1000grain arrow. Were talking about shooting super heavy arrow weights feeling that you will get more penetration. Nor are we compareing two different bows. Were comparing the momentum of an arrow shot out of the same bow at different gpp.

[Biggie Hoffman]

We sure make this harder than it needs to be sometimes. Ballistics on bows and arrows :-(

GEORGE! OH GEORGE! Will you explain this to me in oldtimers?