Paul L Mohr

I believe I said this not Arthur, I think Arthur shoots heavier arrows than that. When I did this test with MY bow and MY set up it showed I had a maximum efficiency at around 450 grns. Every set up will be slightly different.

And my tests had nothing to do with performance on game. They were simply measuring the amount of penetration (depth) I could get with different arrows in a consistent medium. The problem with any of these tests into a medium like foam or any other target is that the thing is designed to stop an arrow by use of friction. You can't quantify things and say that if I shot an arrow with X amount of KE and momentum I would get this amount of penetration. And if I doubled that figure I would get twice the penetration. It won't work that way, I tried.

I really wanted to build something that would measure the amount of force that the arrow had when it struck something.

What I did notice is that there is a definite difference between light arrows and heavier arrows out of my bow. And I don't need to measure it to know it. When I was doing some tests shooting at a 3-D target you could hear and see the difference between the two arrows at 20 and 30 yards. The heavier arrows hit the target much harder and actually rocked it after the shot. The lighter arrows (300-350 grns) didn't hit as hard or move the target. This tells me that the heavier arrows carried more energy to the target for sure.

That being said I have seen a 350 grn arrow moving in the low 200 fps range with a good sharp head zip right though a deer and stick in the ground from 20 yards. And this was from a bow with 50 lbs of draw weight and 26 inches of draw. There are an awful lot of variables to how a particular arrow will penetrate in live game.

I will be honest, I haven't read DR Ashby's report, I already know what works for me and I don't plan on hunting cape buffalo or elephants. I might read it just for the heck of it when I have time though.

Paul

davepjr71

Sorry Paul and I apologize to Arthur for naming the wrong person.

I've read more of Ashby's report and found it interesting reading.According to him the lighter and faster arrow generates more friction and therefore should stop faster in a target made to use friction. However, if the lighter arrow has a smaller diameter then this negates the additional friction from the faster arrow. With my set-up the taget moves just as much and is just as loud when it strikes.

The lighter arrow actual has moreKE than the heavier one. You can use a chrono to get your velocity and you know the weight of the arrow. Therefore, you can calculate the force.

I definitely agree with you that I know what works for me and really do not need somone else telling me that it's not good enough.

Straightarrow

Paul, you've pointed out the key. Foam target penetration has no correlation to penetration on game.

This is something that is very obvious if the weights are significantly different. I've been using arrows around 650 grains out of my compound while shooting 3D. Some of the guys I shoot with are around 380-420 grains with their arrows. The difference in target movement is so obvious that everyone notices it right away. It's not a little more movement - it's a lot more. And I'm using a slightly lighter draw weight than these guys!

If someone wanted to determine KE and momentum on some arrows, it does no good to measure it two feet from the bow. The crony should be set at 25-35 yards or whatever your maximun range is. Heavier arrows will be far more impressive at hunting ranges. If you're worried about such numbers they are only relavent at whatever maximum distance you might shoot at.

Oh, and I'm not saying, and never did, that what works for someone isn't good enough. I'm simply saying that heavier is better when it comes to arrow stability and penetration on game. If someone gets a thrill out of shooting a fast arrow, I have no problem with it if they know what they're doing. My real hope is that anyone who in unsure of how to best control their arrow or who may be shooting low poundage bows or very short draw lengths, are aware that heavier arrows will give them an advantage.

Arthur P

The device you want to build has been around for a long, long time, Paul. It's called a ballistic penduluum.Youmight find these instructions useful.

http://www.g4tv.com/techtvvault/features/45094/Build_a_Ballistic_Pendulum.html

Straightarrow

Hey Arthur, that is one cool device! Every bow shop I've ever been in, has a crony to measure speed, but none have ever had anything to measure force. I could see a company marketing something like this with a range on it to use as a guide to determine if your arrow had the force for killing particular animals. Plus is would be so easy to shoot at whatever distance you were hunting at. Talk about a device that would be a whole lot more useful than a crony!

davepjr71

It would be cool to be able to see the force of your arrow. However, I'm not sure using it to determine if your arrow has the force to kill a particular animal would be practical. Who and how do you determine that? I'm not being sarcastic about this. It's an honest question.

A very sharp broadhead on a light arrow out a slow bow can kill a lot of things. Ashby's main point had to do with what he considered penetration. To him, it was passing thru the medium. However, as long as you strike vitals you do not need to go thru the animal. Also, do you decide this by saying the arrow has to be able to go thru a shoulder blade on the entrance side of the animal? To me this is not a good shot and therefore, wouldn't be considered in my criteria.

Setting up a criteria like this would be almost impossible.

And Arthur, you beat me to the ballistic pendulum. It's been around for a long long time.

BobCo19-65

Paul, I'm having a little trouble with the quote. Are you saying a bows efficiency isa direct measure of penetration?It definately is part of it. A bows efficiency as I understand is the the bows ability to transmit max energy to the arrow and not loose energy to other things such as vibration, noise, friction, etc.. A heavier arrow is able to absorb more of the bows energy then a lighter weighted arrow thus making the bow more efficient.

Arthur P

Yeah, it's a good device that shouldn't have been laid aside. But it was totally forgotten when the chronograph was invented. Companies that marketed the penduluum have already come and gone.

A fella named Benjamin Roberts inventedthe ballistic penduluum way back in the mid-1700's as an efficient way to test the quality of black powder. Early archery researchers back in the early 20th Century - guys likeHickman, Klopsteg and Nagler - didn't have chronographs, so they used the penduluum. Fred Bear even wrote a bit about his experiments with the ballistic penduluum in the 'arrow selection' section of his The Archer's Bible.

Now most people have never heard of it.[&:]

Of course it's not a good shot, Dave. Nobody with a lick of sense aims at the shoulder blade with a bow-n-arrow. But'stuff happens.' And 'stuff' is more likely to happen - and happen more often- with guys who are less experienced, less skilledand less knowledgeable. I think a little extra arrow weight, a little extra penetration potential, would help make a bad situation come out with a better conclusion in some cases. And, in my book, even one less wounded and lost animal is reason enough for a minimum arrow weight regulation.

If you only consider perfect shotsunder perfect conditions in your criteria, then you're right and I'm wrong. When you add in the unfortunate fact that perfection isn't something you can expect every time...

My choice of hunting gear is ruled by an old proverb and it has never failed me:"Expect the best, but prepare for the worst."

BobCo19-65

Me included. Thanks for the link Art.

davepjr71

That's amazing that most people have never heard of it. I tried to do an experiment with my .44 mag when I was younger with the ballistic pendulum. May have to set one up for my arrows.