rib breaking force

[Shawn Leonard]

I should say that guys who shoot lighter weights 45-50#s really benefit as they can shoot 9gpp. with high FOC and still have an arrow that does not start dropping like a log past 20 yards yet penetrate as well or better as than an arrow weighing 10-11gpp. without the high FOC. Shawn

[ccarp00]

Tbone I wish someone could ease your mind on this but I think the problem is it is too much of an opionated question.  Kind of like the age old question is the .243 an adequate deer rifle.  To the folks who have filled the freezer with them for generations they are more than enough for the advocates of you have to a 7mm short mag its unethical.  If you got good arrow flight and sharp broadheads you have enough to kill 99% of elk 99% of the time.  It don't matter if you use a 100lb recurve some animals are just harder to kill than others.

[JImmyDee]

Arithmetic time!

Using your 610 gr and .40 lb-s numbers, I figure your arrows's moving at 147 fps and carrying 29.2 lb-ft force.

Presuming the same bow efficiency:
650 gr @ 142 fps gives .41 lb-s momentum;
700 gr @ 137 fps gives .43 lb-s momentum;
750 gr @ 132 fps gives .44 lb-s momentum.

But you probably know that -- and you probably also know that's still a lot less than the .57 lb-s Ashby says is "adequate" for big game with a good head.

Shawn makes a good point: skinny, high FOC arrows  penetrate better.  Maybe a .400 deflection skinny carbon shaft with 325 gr worth of insert plus adaptor plus a single bladed, single bevel knife up front is just what you need.

[T-Bone]

Thanks all for your input.  Jimmy, thankyou for the momentum numbers as well. Was Dr. Ashbey's .57 figure pertained to elk size game?  That just seems very high because it would take a pretty heavy setup to obtain that value.

[RC]

I killed a boar this year that weighed 200 lbs. It was a swamp boar and was not real heavy but had 1 1/8 thick sheild. I shot him with a 2020 and magnus I with an aluminum adapter shooting a 50lb homemade longbow ,arrow was around 600 grains I believe. It was a pass through. I can`t picture and elk being much tuffer. Even better if you shot a smaller cut broadhead like a grizzly.RC

[JImmyDee]

Originally posted by T-Bone:
Was Dr. Ashbey's .57 figure pertained to elk size game?

Yeah, how do you quantify this stuff?  What's "big" and what's "adequate?"

There are lots of anecdotal accounts of harvests with a wide variety of gear, but Ashby seems to have compiled the largest data set and devised good analyses.

If I remember correctly, he said big was up to zebra-size and adequate could be counted on to penetrate despite hitting heavy bone.

Now, zebra v. elk?  Scapula v. rib?  Time to arm wrestle!

[j yenney]

I use a 2018 easton at 28.5" with a 100gr. 2 blade broadhead and shoot a 52# bow and have never any problems killing Elk with complete pass thrus, Moose should be even better seeing there ribs are spread a little farther apart. I'll let you know on moose next season, but I have no doubts.Let's not try to get into the big cannon theary about what it takes to kill an elk.

[Tree man]

I appreciate Dr.Ashby's work. I read it with interest. There are things to be gleaned from it. However, even in Dr. Ashby's attempts to approach things scientifically and analytically he suffers from the same malady as most of us-preconceptions and a fixation on his own percieved needs.
To say that X momentum is required in testing to penetrate Water Buffalo ribs 100% of the time so X momentum should prove adequate on all "lesser" game is logical. On the otherhand to Say that since X momentum was required in testing to reliably penetrate Buff ribs X should be required for all game is....well...bizarre. I have no problem with Dr.Ashby or anyone else making a personal determination to never shoot arrows less than 650 grains or 700 grains or 900 grains etc. and to always maintain momentum values above a given level for all their hunting. Just don't bind that on others. We have several thousand years of men shooting animals with sharp pointy things from bent sticks and the animals dying and being eaten. Check out Native American Indian tackle. Silly injuns. They kept shooting animals with light to medium weight arrows from primarily 40-60 lb bows-many of them with short drawlengths and then, just cause the animals died, they thought it adequate.
My preferences run to relatively heavy arrows and sharp two blade heads (Not only am I somewhat influenced  by Ashby's research it correlates with my own experience in many respects and heavy 2 blades are the choice of many people I repect....but others I respect choose lighter arrows and multiblade heads. When I look back over my own limuted experience I have to note that lighter arrows and 3 and 4 blade heads did not fail me when I used them....I just gravitated to the percieved superiority of more momentum and 2 blades and found that satisfactory.
 The truth is everything works and everything fails. Terminal ballistics whether with gun or bow simply cannot be reduced to formulae and thus achieve some ultimate truth. I learned to distrust the magic numbers when I was a teenage gun nut. I read various experts (Who didn't all agree) and then watched animals falling over when shot with projectiles possessing 1/10th of the "required" kinetic energy, or momentum or Taylor Knock Out Value or Keith's "Pounds feet". All these statistical mental gymnastics make grist for the writers mill, entertainment for the winter doldrums and help us to think...but don't stop thinking. Since multiple models and theories work in actual practice it may be prudent to quit worrying about it and go hunting! In fact I would like to avance the theory of quantum terminal ballistics-To whit, researchers may observe the results they anticipate. Therefore, trust your gear and expect animals to die when shot ...and they WILL!

[T-Bone]

I truly respect and am awed by the research that Dr. Ashbey has done.  But the trad bow it takes to generate .57 momentum is substancially higher poundage than 90% of my trad bow elk hunting aquaintences here in Colorado. I know lots and lots of hunters who routinely kill elk with bows that cannot achieve .57 momentum within reasonable grain per pound ranges.  The majority of elk hunters I know shoot 55-60# bows.  With my setup being which I believe to be on the light side of adequate for elk hunting, I was just wanting to know if anyone had any educated guesses for the momentum required to poke through elk ribs so I could choose the best arrow weight to achieve this goal.  I appreciate all the input, and did not mean to stir a debate.
Thankyou!!

[mmgrode]

If I was you I'd shoot for 600 grains or so and try to point load it for a high FOC.  Use a razor sharp two blade and with this setup there should be no worries as long as you don't hit scapula.  Good hunting, Matt

[mmgrode]

You could think about using a recurve also.

[khardrunner]

Treeman,
I think there is a significant difference between what was acceptable when Indians were hunting with light tackle and what we are looking for today. Ethics doesn't come into play when you are talking about survival. Today we are concerned with 1 shot 1 kill...swift and efficient. It is illogical to draw comparisions for that reason. Sure, just about anyone can kill an elk (or other big game) with a 40lb bow and 300 grain arrow. Just keep chasing and shooting until the poor thing gives up! But that isn't what we are about. That is why Dr. Ashby and others feel that it is important to have the right equipment available to do what we love (shoot traditional) while making sure we have not comprimised the integrty of the hunt.

Granted, there are many circumstances, stories and other experiences wherein game has been taken with less that what many would consider "adequate". However, the point should not be what can I get away with. Rather, we focus on what can we do to minimize our chances of wounding, losing or otherwise comprimising our ethics.

[Orion]

T-Bone.  I think you've pretty much got it figured out.  Your set up is enough for elk.  Centering a rib on the way in on a moose could be problematic.  I've killed a moose with heavier equipment, but realize I won't always be able to use a heavy bow.  If I were in your shoes, I'd have at it.

[Brian Krebs]

at what distance is the energy talked about being measured?

 How does distance effect energy statistics?

[jimbob91]

Agreed Brain.If we 're talking 10 to 20 yrds and a sharp 2blade does it really matter?

[khardrunner]

Distance does not change energy, it only limits what is available for use in penetration. Outside of the fact that momentum is a better measurment for penetration ability than kinetic energy, the major effect that distance has is a change in velocity (a factor both in momentum and kenetic energy). It will depend on initial velocity and air resistance of the arrow (friction).

Interestingly, once the arrow has left the bow, the mass becomes irrelevant in determining velocity (any time during flight prior to impact). Distance is only relevant because of time spent under the influence of friction, paradox, and other velocity sapping phenomena.

[jindydiver]

Originally posted by khardrunner:
Distance does not change energy, it only limits what is available for use in penetration. Outside of the fact that momentum is a better measurment for penetration ability than kinetic energy, the major effect that distance has is a change in velocity (a factor both in momentum and kenetic energy). It will depend on initial velocity and air resistance of the arrow (friction).

Interestingly, once the arrow has left the bow, the mass becomes irrelevant in determining velocity (any time during flight prior to impact). Distance is only relevant because of time spent under the influence of friction, paradox, and other velocity sapping phenomena.

Of course distance changes energy. If the arrow sheds speed because of friction it is also losing energy. The only way this could be false is if the arrow somehow picks up weight as it slows (and we know that can't happen). When you say that velocity is "a factor both in momentum and kinetic energy" you are saying exactly that, the longer an arrow has to travel the less energy it will have when it reaches it's target.

[jimbob91]

So what your saying is the same arrow out of the same bow will penetrate the same from 10 to 20yrds?No lets say 10 to 30yrds,your saying that same arrow will have as much energy at 30 as it does at 10?