bigbulls

Redline. Take brand "X" bow and two arrows. One that weighs 350 grains and one that weighs 500 grains. Shoot them both through the chronograph and calculate the KE. The heavier arrow will have more KE and momentum. This is directly related to the ammount of time that forces are being applied to the arrow.

Wrong. All of the bows stored energy is not transfered to the arrow. It is also transfered to the riser, limbs, the cams, the string and cables, your hand,etc... etc...

Itisn't as simple as you are trying to make it. The ammount of time that "X" ammount of forces are being applied to the projectileabsolutely plays a part in available KE and momentum.

As the string is released the stored energy is being transfered to the arrow. The longer that the projectile is having the available energy being transfered to it the more energy it is absorbing. This is true in rifles as well. Or any moveable object for that matter.Given the same cartridge being fired out of the same gun a heavier projectile remains in the barrel longer and the pressures (say 60,000 psi) insidethe barrel are able to exert their forces upon the bullet for a longer period of time which will give the heavier projectile more KE and momentum.

That's becasue you are not using the correct equation. I don't know exactlywhat the equation would be but in your equation it only accounts for the velocity after the available energy has been transfered to the projectile.

98Redline

OK, lets go under the assumtion that I am completely wrong.

How is it that archery programs (Archers Advantage, TAP, etc...), which use the correct physics formulas, will show nearly identical KE for a given bow even as arrow weight changes grossly?

bigbulls

Nearly identical isn't identical is it?
Go shoot a 350 grain arrow and a 500 grain arrow out of the same bow through a chronograph and calculate the KE numbers and tell me which one has more KE. The 500 grain arrow will have aproximately 1 - 3 more foot pounds of KE.

Look at a rifle since it is dealing with far greater forces than a bow and the results are much more noticable.

Assume 55,000 PSI chamber pressure a30-06 will fire a 180 grain bullet at a lower velocity than it will a 150 grain bullet but the 180 grain bullet will have aproximately 100 foot poinds more KE at teh muzzle than the 150 gran bullet. That 55,000 psi is able to do more "work" on the heavier bullet becasue the forces are being applied over a longer period of time.

AllenRead

If they are going the same speed the heavier arrow will have both more KE and more momentum.

I think that you mis-wrote this as I agree with everything else you posted. I've just been reading reports of Dr Ashby's research and am climbing on the heavy arrow bandwagon.

If I interpret the recent article in Traditional Bowhunter magazine, my 60 # Justice @ 26" DLshooting a 682 grain arrow will penetrate a water bufalo's ribs on one side, but not the other. However, the same bow with a 384 grain arrow will not penetrate ribs, even though it's going about 50 fps faster.

I have a little more testing of my own gear before completely I buy into this. But Ashby's research is pretty compelling.

note: the article's formula's seemed to be off by a factor of 10. My bow may be shooting 17 foot pounds, but it is definitely not shooting 170 foot pounds.

passthru79

I agree that a heavier arrow will have more momentum and KE than a lighter one at the same speed, but what I am disagreeing with is the fact that people seem to think that you absolutely have to have the heavy arrow to get them job done. Depending on the situation it is not always the best option.

AllenRead

I agree that ultra heavy arrows are not absolutely necessary to take anygame in North America. It's been proven many thousands of times since carbon arrows became available.

However, I can't think of a situation where the better penetrating arrow isn't the best option. Maybe when shooting at unknown distances, but most of us are shooting from stands or blinds and have range finders.

Can you tell us what kind of hunting situation thatyou are referring to?

I don't mean to bash or argue, just trying to learn.

Thanks,
Allen

Straightarrow

I don't see where anyone suggested that. It's obvious that there are many ways you can kill animals. What some of us are saying is, the heavier arrow will do a better job of penetration in less than perfect hits and that trajectory is not an issue in most hunting situations - close range and the yardage can be pre-determined.

Like AllenRead said, it may not be, but I can't think of a hunting situation where I wouldn't prefer the heavier arrow.

bow_hunter44

I know one thing, I didn't imply anything about good or bad as far as arrow selection goes. What I did say was that kinetic energy and momentum are not the same thing! On the, unfortunately, rare occasion that I get to the pro shop I hear the patrons talking about KE as if it is the paragon of all virtues. WhileKE is a wonderful thing to be sure, it is not the only thing. Leastwe forget our old,often forgotten friend -momentum!

passthru79

In responce to AllenRead, Im not sure what it is your hunting but I have never had an issue with lack of penetration on white tail deer. I have shot a couple that have field dressed 250 plus pounds and penetration wasnt an issue using a 365 grain arrow at around 300fps. I dont see the point in going with a super heavy arrow to get better penetration if you dont need it. Stay with the medium weight arrow that is fast and benefit from the flat trajectory. You said you couldnt think of a situation where better pentration wasnt the best option, put the arrow where it needs to be and it shouldnt matter. If you dont have time to range an animal or it happens real fast, that faster/flatter shooting arrow will help keep it in the kill. Just for an example, I shot a deer last year that would have probaly weighed 275 or more on the hoove. 50 yards quartering hard away. The arrow entered just behind last rib and stopped on the leg bone of the offside shoulder. I was shootinga easton axis shaft tipped with a wasp boss bullet for a total weight of 365 grains at approximately 310 fps. Do you think a 500 grain arrow would have snapped that leg bone and blew threw it, I doubt it.

passthru79

I know Bow Hunter44, but you did say something about the heavier arrow being the best choice because it carries more momentum. I agreed with you about the KE and Momentum difference. I disagreed about the heavier arrow being the best option.