Testing arrow penetration with 2 different setups

[TxAg]

Originally posted by Nativestranger:
Tests done at 10 yards. By now I think some of you would have guessed the arrows are shot out of 2 different bows. (It's physically impossible to shoot a lighter arrow with higher KE out of the same bow) I repeated the test by shooting the 2 arrows from the same bow and both arrows penetrate exactly the same every time.

Are you positive? The formula for KE squares the  velocity measurement so a lighter arrow (faster arrow) should increase the product vs what a heavier arrow would do (only increasing mass which is not squared)


Your statement makes sense if you replace KE with momentum.

[Nativestranger]

All bows are more efficient with heavier arrows. Kinetic energy usually increase with arrow weight. This can be negligible with highly efficient recurves or hybrid bows but significant with less efficient longbows or selfbows. The bow in setup B tested with a 360 grain arrow at 173 fps. So that's about 2.7% increase in KE over the 300 grain arrow. Btw you are partly right, momentum always go up more rapidly with increase arrow weight.

[last arrow]

What was the hypothesis you were trying to prove?

There are to many variables for me to make any conclusions from this test.  Different bows, highly variable penetration medium,  friction on the arrow, potentially different tune, etc.  For example, a slight dulling (or blunting) of one of the tips would make a big difference on a medium like ply wood.

[ChuckC]

Good job.  but this has been done before.  Similar results.  If I ever draw a tag to hunt plywood, I will most certainly use a lighter arrow.  

Actually, try it using a blunt.  If your bow generates enough force, the blunt will punch a hole in the plywood, not forcing a point through but blowing a full sized hole in it, which of course provides for less friction on the rest of the arrow, which will blow on thru.

Thank you for your test.
ChuckC

[DanielB89]

I have posted this before, but i think you'll find it very interesting.. IF you take the time to watch it.  

Part 1
 


part 2
 

[Nativestranger]

This test is trying to determine if Momentum or Kinetic energy will better determine penetration potential in an arrow. Yes it isn't done with real flesh. Never claimed that this will represent an exact hunting scenario. I used what's on hand (which happen to be pretty uniform throughout) rather than sit around argue about theories without doing anything to prove them. Well lubricated soft tissue isn't going to be the issue for most arrows with a sharp broadhead anyway. Its the hard stuff like bone that grips the arrow shaft tight that's gonna limit penetration in most cases. Take this test as what it is until I can get better test materials.

[Orion]

Dr. Ashby already determined that momentum is the better predictor, using real animals no less. His research is on this site.

[LBR]

Not just Dr. Ashby, but lots of Professional Hunters/Guides, along with the hunters themselves.

Depending on the animals, there can be more to consider than flesh and bone;  i.e. feral pigs.  The big males have a "shield" of gristle that isn't like bone, or foam, or plywood, etc.  It's like...gristle.

Water buffalo (haven't hunted them, but almost went and studied it long and hard for over a year before an injury cancelled my trip for me).  You may have to penetrate a thick layer of mud/dirt, hair, and over an inch of hide just to get to the flesh and bone.  That's going to be a really tough test medium to replicate...but even if you did, we already know what the guides have found works best.

[Zradix]

Nativestranger ...

I think I understand what you're trying to do.
TxAg has a VERY good point.
As you said yourself...bows are more efficient with heavier arrows..ie KE changes with different arrow weights.

KE measures the energy required to put something in motion....in a 100% efficient machine/environment you'd really have good #'s to work with...bows aren't 100% efficient in propelling an arrow.
So you end up with this "fuzzy" number that doesn't really mean much in the world of hunting.

also...aaaa heck...just read what others have tested..it's all been done and figured out and will be a lot easier on ya bud.
No reason for me to regurgitate it.

If ya really want to know which arrow has more penetrating power (giving they're all tuned the same etc, etc,etc) and want to do it yourself .. just multiply the weight by the speed. The set up with the highest # wins. Much easier...lol

Test those setups/arrows at different yardages and you'll really learn something.

Good luck to ya.  

[Nativestranger]

Speed x weight= Momentum. Speed x speed x weight = Kinetic energy. Right now the setup with more momentum, less KE doesn't seem to penetrate any better even though I initially thought it would.
I have read Ashby tests. But they are inconclusive as to whether KE or Momentum is more important. Shooting the same bow with different arrows will always produce both higher KE and higher momentum on the heavier arrows. And his heavy arrows also has significantly higher FOC skewing results.  
Here's something to think about. If tests were done comparing between a 50# bow and a 30# bow and the 50# bow out penetrate the 30# bow on plywood, then I am pretty sure nobody would question the validity of the test. If the 50# bow out penetrate the 30# bow again on ballistic gel, phone book, target foam. Is it reasonable to assume that it will be expected to perform better on live game? If given 2 unknown bows and one always stick an arrow deeper than the other on plywood. Most logical person will again choose the one that does better. So isn't it funny that all of a sudden this test medium is now invalid when testing arrows of different properties?
Now if anyone can suggest a better test medium then by all means I will try my best to repeat the test with it.

[dnovo]

I can't help but look at every one of these penetration tests. I never see any relevant data.
All the tests are done into some medium that uses friction on the arrow to determine penetration. A light arrow usually wins. Most of the time the data fails to disclose arrow shaft diameter which is the determining factor.
Plywood is a useless medium for any real world scenario unless you just want to play around with shooting holes in it.

[Zradix]

Have fun bud.
   

[Nativestranger]

Looks like Blackhawk and Scott are correct in their prediction. Now to see if I can get insulation foam suggested by JimB.

[last arrow]

I believe this simple test has no value, there are just too many variables.  I can make a 600 grain arrow from a 50 pound bow skip off a plastic bottle  cap just by varying the angle of impact (it only takes being 10 to 15 degrees off perpendicular if the cap isn't anchored). I don't think that proves the combination is not good for hunting.  As the speed of the arrows is different in your test, the angle of impact is different due to different trajectories. The difference in observed penetration is to small to ignore these variables. That's one example.  As I said, too many variables.

I don't think comparing fresh bone to plywood provides much value either.  Its been my experience that fresh bone in up to elk size animals cut/split (ribs anyway) rather than shatter like ply wood.  I believe some one did a post here years ago comparing penetration in fresh deer scapula to dried ones and found that the fresh/split cut also rather than shatter.  Maybe someone remembers that and can provide verification.

If I sound overly cynical, my job requires me to evaluate vendor data to determine whether to include their products in our designs (or whether more testing needs to be done).  In my 30 years of doing this, I have found that most vendors design tests that show their product is better than their competitors rather than to provide usable, more applicable, data. I can't help but pick "test" data apart.  Unfortunately there is no ASTM method to measure arrow penetration in animals to end these debates (then we would be debating the test method).

[JimB]

"I have read Ashby tests. But they are inconclusive as to whether KE or Momentum is more important. "

Read them again.The tests were very conclusive and he goes to great length to show that momentum is far more relative to penetration than KE.

Here is another article that examines this:
 http://www.tuffhead.com/education/formulas_momentum.html

another:
 http://www.africanarcher.com/momentumKENETICS.html

another:
 https://www.qdma.com/articles/momentum-beats-speed-for-lethal-arrow-hits

another:
 http://www.tuffhead.com/ashby_pdfs/ashby%20ours/PDF%20Momentum,%20Kinetic%20Energy%20and%20Arrow%20Penetration.pdf

Some other stuff to consider when shooting in to man made mediums:
diameter is a big deal.Shaft makers talk about a shaft being 5/16" in diameter but actual specs may shoe they are from .287 to over .300.I have shafts in this range and they may be called 5/16" diameter but they are all different and minor fractions of difference in diameter will change the equation in man made materials.

To compare two different arrow setups,they have to be EXACTLY the same diameter.They also have to be the same FOC unless they are 18% or less.

Shaft finish also effects penetration so both arrows need to have the same shaft finish.Dipped shafts (wood grain,camo etc)are a drier texture and don't penetrate as well as plain carbon.

Your heavier shaft shows a carbon collar,which stops against the wood.Maybe the black shaft has one as well,it doesn't show,but if it doesn't,that will drastically skew results.

"And his heavy arrows also has significantly higher FOC skewing results. "

This also is untrue.Many of the tests used standard FOC arrows and when he was testing momentum VS KE,this was accounted for.

Ashby has tested all this stuff to death for over 28 years and $300,000 dollars spent.I've been delving in to this stuff nyself for about 8 years and don't have the time,money or patience that Doc Ashby does but I do run some occasional tests and all of those have correlated well with Ashby's findings.

I can tell you this,following what I have learned from the Ashby reports,using a combination of increased arrow weight,high FOC etc,I have more than doubled penetration from where I started.I'm relegated these days to bows in the low 50# range and these are penetrating way better than my former setups which were 60-66# bows and 9-10 GPP arrows with normal FOC.

Honestly I think your arrow shafts are too different to get reliable results from.If I were testing,I would want both shafts to be black,identical diameters,measured with electronic calipers and any footings or collars to be identical.Again,Ashby has already done this to death.I enjoy testing too but mine will never be as exhaustive as his.

So far,just following his results,my setups have increased in efficiency way beyond what I ever thought possible.

Anyway,good luck with your testing.Some day when I get enough time,a chronograph and a shooting machine,I plan to do some of my own.I spent over 2 years trying to come up with 2 arrows of exactly the same diameter but hugely different FOC numbers plus same diameter arrows with similar FOC but one light and one very heavy.That's not as easy as it sounds but I finally cracked the code.

Besides testing them for penetration,if possible,I'd like to flight shoot them from a machine.We'll see.

[Nativestranger]

Just to clarify some stuff. That's the insert behind the point not a carbon collar. The lighter shaft has it too. Both shaft are the same 5/16 diameter. Within 3% Foc difference.  Points are unsharpened. Shaft finishing doesn't matter as the heavier shaft didn't penetrate past the insert. No angle difference between them as they are shot from the same position to within 2 inches on the plywood. I admit some part of this test isn't perfect. Shooting at a non homogeneous medium like a live animal will give inconsistent results as well depending on where you hit. If the the theory that momentum and weight significantly outweigh KE, it should still show here without the need to formulate excuses. I often hear claims that light arrows gives me only 2" of penetration on animal or bounces off deer while heavy arrows pass all the way through. That's of course quite serious claims made in totally non controlled test environments. If that's true then it should show up in my test without the need to split hairs like small angle differences, shaft diameter... so on. Are any tests done other than Ashby that supports the momentum theory? The only 3 other test I can find are from Ken B, Ike and Ripfletching and all those concludes weight doesn't matter much in penetration.

[monterey]

Originally posted by Nativestranger:
Setup A 400 grain arrow 151 fps

Setup B 300 grain arrow 185 fps

Speed verified with chronometer. Setup A has 33% more arrow weight and ~10% more momentum. Setup B has ~15% more KE. Which do you think will provide more penetration into hard medium like bone? Will be testing them on 3/4" plywood.

In my response to the original question I gave the edge to the heavy arrow.  That said, and at the risk of seeming a sore loser, I'll throw in my thoughts on your results.

The flaw, IMO, is the unrealistic velocity spread.  While tuning considerations may not have allowed shooting from the same bow, they both should have been chronographed from the same bow and then those velocities matched when shot from a bow to which they were matched.  

I have extensive chronographed data from eight bows with draw weights ranging from 38# to 46# with each bow shot with two arrows.  One is 525 grains and the other 675.  The velocity spreads between the two are mostly in the single digits.

A real world comparison would have had your 400 grain arrow running at around 173 to 177 fps.

[Nativestranger]

The 2 arrows are shot from 2 bows. 400 grain from a 37# bow. 300 grain from a 40# bow. I draw them to my draw length of just under 26.5". chrono tested them and set it up this way so the 400g arrow has more momentum/ weight and the 300g more kinetic energy. Yes you right that the velocity spread is quite big. But that's how you get the KE up for the lighter arrow. There's no other way to it. Then again if Momentum and weight (as what was previously thought) is the deciding factor then the velocity difference should not matter.

I might add that I also tested both arrows from both bows.

*The 40# bow tested 164 fps with the heavy arrow
*The 37# bow tested 173 fps with the light arrow
*The same bow penetrated the same with both arrows.
*The heavier bow always penetrate deeper than the lighter bow regardless of arrow weight.

[ChuckC]

I believe I see what you are getting at NS but to me it appears you are supplying a situation that is contrived and not based on fair comparison at all.

Just because one is heavier does not mean you can just toss it against the wall and expect it to knock it down.  There comes a point in the experiment where the difference in speed is so great that there is no competition, and what then does that really show ?

Your testing was appreciated. Thank you. Points were made and I was drawn to think about the actions and results.  

I will, however, still be using 580 grain arrows for elk season this year and wishing they were just a wee bit heavier.

CHuckC

[JimB]

Thanks.I understand what you are saying but again-5/16" is an industry term that spans a variety of outside diameters.Usually,these shafts have an inside diameter of .245-.246" but the out side diameters vary widely.Caliper measurements!

Personally,when I test penetration,I want a medium that the arrows will go deeply into-like 2/3 of the shaft length.This way,differences are more obvious.I've only been testing this stuff for 8 years but my findings are different than what you have come up with from shooting 2 sets of arrows from 2 different bows,into a hard medium.

"Are any tests done other than Ashby that supports the momentum theory"
Honestly,I get this all the time.I assume you did not read any of the articles that I gave links to.It's funny how a few minutes of video on Youtube,trumps 28 years of testing with all details of the tested arrows shown.He doesn't say a 300 gr arrow vs a 400 gr arrow when it was actually something else and if the arrow diameters were slightly different,that was noted.

My tests show that increasing arrow weight by say 10%,increases penetration 20%.If you bother to read,you might understand why this occurs.

What is seldom discussed about the Ashby reports is that during those 28 plus years,he logged data on 627 plus big game animal harvests of his own plus some from other hunters and cross referenced that data with the penetration tests.If ever saw the data sheets and criteria for this,it is thorough,way more detail than I'd have patience to provide.But yeah,a couple unknown guys shooting a handful of arrows with sketchy specs,om Youtube,for sure,has more relevance.This too,has been done to death.

"I have read Ashby tests. But they are inconclusive as to whether KE or Momentum is more important. "

"And his heavy arrows also has significantly higher FOC skewing results."

These statements are incorrect and you seem to have sloughed over them.

Good luck with your "testing"