arrow penetration question

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courtgreene

courtgreene

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So, I've taken up bow making and decided that this year I want to use one of my own to drop a deer. As a hunter, not redneck, that means I have to see how the arrows penetrate to make sure I'm shooting the right bow for the job. One of the bows has a much heavier draw weight, but the other is much more accurate. On to my problem... both bows penetrate the same amount on my target (40 dollar walmart foam block). I'm talking a difference of less than a millimeter. I'm perplexed. I think shooting the same arrows, the stronger bow should penetrate further, but that's not what happens. Given the situation, I have no idea which to shoot for deer. (if it matters, they are long bows with magnus broadheads).

Any thoughts?

Thanks.
 
I think shooting the same arrows, the stronger bow should penetrate further
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No way two bows of different poundage can shoot the same exact arrow dia & length, or in other words Spine, or stiffness.

Penetration depends on several things.

Could be the arrow is still flexing back and forth out of the stronger bow when it hits the target do to not enough arrow spine for the power of the bow..
Whereas the less powerful bows arrow has already straightened out and is flying straight on to the target at the range you are shooting them.

The heavier bow will have to use a stiffer arrow spine to shoot right if the same arrow shoots right in the less powerful bow.

All arrows do some unbelievable convolution's for the first 20 yards or so until they settle down and fly right.

Anyway, your only truly reliable test would be to shoot both bows over a chronograph and see which one is faster.

And find the right arrow spine to use in each of them.

rc
 
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The arrow out of the "heavier/ faster" bow is not as stable when it hits your foam target, period.
As for deer hunting, penetration is NOT an issue from modern equipment, that arrow stability though, can mean the difference between a good hit and a miss, or worse yet, a bad hit.
 
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Thanks, I thought that the arrow's not flying straight yet may have something to do with it. Matrem, this is not modern equipment, which is why I'm worried about it. is there any inanimate object (like a watermelon or something, just throwing that out there) that you would suggest that would be a good test object, to draw comparisons to deer? Chronographs are not cheap, and I'm on a budget you see.
 
Water filled gallon milk or windshield washer fluid jugs would more closely apporimate a deer then a watermellon.

I'd say if you can shoot through 3-4 water jugs, a broadside deer would be no problem.

rc
 
I'd call razor sharp Magnus broadheads "modern".

As long as you're pulling 40-45 lbs minimum, get "stable" arrow flight, and hit a bit behind that shoulder about a third of the way up or so, I'm betting venison is in your very near future.
 
Sorry Matrem, I thought you meant the bow. Thanks everyone, water jugs will be shot tomorrow!
 
How far are your arrows penetrating the foam block? How heavy are your broadheads? Are the arrows Wood, Aluminum or carbon fiber? For me with 140 gr. broadhead at 195 fps, Aluminum shafts (2117) I get complete pass through double lung (broadside) with the arrow on white tail. My equipment is from 1985. What pound are your long bows?

DMH
 
DMH, about seven inches. Broadheads are 100 grn and I'm shooting carbon arrows (I generally just refletch my compound bow's arrows with feathers when I shoot out the vanes on them, like I said, budget), The heavier longbow is sixty pounds, and i haven't weighed the other.
 
Go with the bow you shoot the best. No question if you are getting 7" of penetration into a pretty new foam block. A broadside deer will be no problem. Pick your shots and watch your distance all will be fine.
 
Courtgreene, 100 gr. with 60 pounds will be no problem with a deer. I agree with what was said earlier and shot placement is the number one concern. With that set up you need to know what you are comfortable with. For me my limit is 40 yards. The water jugs are a good idea if you really want to test penetration. Chronographs can be had for $100.00 and can be a useful tool if you reload or have additional needs for it. Some ranges have rentals for members. Ask around you may be surprised at who has one to loan you. Archery shops can verify pull weight and velocity, and I have found the Ma and Pa shops to be friendly and reasonable. My goal when practicing at a given distance is all arrows in 5" group or don't attempt a deer at that range.

DMH
 
the draw length effects the energy of the arrow. The bow with the heavier draw weight may have a shorter effective draw length because of a longer brace height.

Brace height also effects how easy a bow is to shoot accurately, I think.

Bob
 
IF you are new to bow building...I would wager there are significant differences between the two bows besides draw weight alone.

You mention that one bow has a greater draw weight than the other, but SO much more is at play.

Unless you have carefully tillered both bows, they can/will have distinctively different force draw curves. A much lighter (draw weight) bow can easily be many times more efficient than a heavier (poorly tillered) one.

Other potential problem areas (per your description) are:

1. Arrows not properly spined for at least one of the bows. (poor arrow flight affects penetration).
2. Brace heights different. (affects draw curve and stored energy).
3. How close to center-shot the two risers are, differences in strings, your form, etc....
 
COURTGREENE, Correct me if I'm wrong, but from what you have posted you already have and use a compound bow, the two new long bows you have made yourself. If you are getting into making bows a chronograph will be a useful tool. Being able to measure draw length and draw weight would also be a plus. As some of the posts are suggesting, matching the components is important as far as arrow shaft strength. I do not know what level you are at as far as understanding the number system on arrows. Aluminum and carbon fiber use different number systems. I do not use carbon fiber, and do not know that number system. You could use sheets of paper to shot into at the same distance and see if the arrow produces a nice round hole or if it rips a slot, indicating the arrow was wobbling. When shooting into the foam see if all the arrows look straight or if the fetched ends are sprayed (looking like a dozen roses in a vase).

David
 
Flintknapper, I believe you nailed it with number three. The heavier bow was my first... i've made six others between the two and have learned a lot along the way, but of course always want to learn more. Part of that learning process has me centering the riser better, and also giving myself more of a shelf so that I'm not shooting around the bow as much. I believe the lighter bow (it's not THAT much lighter, I'll weigh it one of these days) is just shooting straighter and that's all there is to it.
Getting back to what was said earlier in the thread, I happened to have water jugs in my garage for my next trip to the range... I lined them up and shot an arrow right through them. Thanks for the tip RC.
 
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