Testing arrow penetration with 2 different setups

[Nativestranger]

Like I said I did test the 2 arrows from the same bow. Please understand I am not doing this to prove a point or trying to promote light arrows over heavy arrows or the other way round. I personally always shoot over 11.7 gpp - 10.3 gpp arrow weight from my bows. They shoot sweeter that way. I am simply curious to the science of momentum vs energy and decided to do some personal testing and share with you the results. Take the test as what it is. Another set of data. Thank you for suggestions and pointing out the limitations. I will also look over your links and Ashby test reports in more detail.

I did read up those links. They get their info from Ashby. I would like see independent and real world tests.

[Nativestranger]

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

That's quite substantial. If true then it should be easy to prove. It didn't show up in my tests when shooting the 33% heavier arrow from the same bow. But I will get another softer test medium to try.

[Arctic Hunter]

Would you rather get hit with a 30" wooden dowel or a 30" piece of rebar?

If I can keep arrow speed reasonable, I'll take the heavy arrow every time. I've seen the results of using both (especially in my wheel bow days). It's worked for me this far.

Others may have had different experience.

[monterey]

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.
 

Of course it matters!  :eek:  

Measure momentum or measure kinetic energy.  Velocity matters!

I dug through some stats of a test I did about this time last year.  I chronoed eight bows with two arrows.  One is a 520 grain the other a 650 grain.  Both cedar, both full length/same length, both fletched the same.  Out of eight bows here is the velocity differential that I got from these two arrows.  The average of four shots for each arrow.  The bows were all weighed on my scale and the scale checked for accuracy with a 45# weight.  the first velocity is for the 520 and the second for the 650.

bow one    28#  153-146 = 7
bow two    30#  139-131 = 5
bow three  34#  149-144 = 5
bow four   46#  164-156 = 8
bow five   44#  170-163 = 7
bow six    40#  163-154 = 9
bow seven  37#  153-146 = 7
bow eight  35#  165-157 = 8

I doubt if many bows will produce significantly different results, yet your test velocities were spread far beyond what is typical.

So, I then went to the range alongside my house with bow number six.  Selected because it is what I will shoot this year for hunting season and also because the two arrows tested below fly equally well from this bow.  Once again, these are POC shafts full/equal length, near identical fletch, identical poly finish on the shaft, both 11/32", one with a 190 grain head and the other with a 145 grain head.  Obviously, FOC will not be the same.  The shaft weights were 575 grain and 525 grain.  Fifty grains difference and with a rather low percentile difference since they are both fairly heavy arrows compared to the 300 an 400 you shot.

I shot seven shots with each into a new foam target that had had only five shots into it prior to this test.  None of the test shots came even close to any pre existing hole.

So, I measured and averaged the seven shots with each arrow.  They were shot alternately so that there was not a shooter fatigue problem or a creeping variation in shooting form.

Came up with this:

575 grain arrow average penetration 10.27"

525 grain arrow average penetration  9.71"

I suggest that you find a bow that will shoot both arrows equally well and do another penetration test.  I think your results will be different.  Or, you can send the arrows to me and I will sort through my cache of bows for one that shoots them equally well and do this same test.

So, season opens in less than two weeks and I just wasted a shooting session on this!      Gotta get back down to business.  

[Nativestranger]

My velocity spread is typical for bows with decent efficiency. Again the numbers for the 40# bow: (36# @ my draw)
300g 185 fps 8.3 gpp 23.9 ft.lbs KE
400g 164 fps 11.1 gpp 22.8 ft.lbs KE

As you can see the 2 arrows are almost 3 gpp difference in my case and it gained about 21 fps going to the lighter arrow. It also lost about 5% KE and dynamic efficiency. Velocity gain about 7.5 fps per gpp. Very typical value for short bows with highly reflexed limbs. I have seen some bows gain 9 fps going from 9gpp to 8gpp. Of course with some bows the velocity gain with lighter arrows will be less. That doesn't mean it can shoot both arrows equally well. Rather it means the bow is inefficient with light arrows and energy drops quickly with arrow weight. Example straight limb longbows over 66". Hand shocky with light arrow and always chrono about the same with different arrows. With different bow designs, penetration behavior may be entirely different from mine which I forgot to mention. By all means shoot what works best.

[Nativestranger]

Your 2 arrows are 50 grain difference and almost all that is the point weight. Vastly different FOC and dynamic spine may have cause the penetration difference. I used both heavier point and heavier shaft on the heavier arrow.

[Zradix]

I gotta unfollow this one..
Have fun gents.

[ChuckC]

I think it can be said that any arrow of reasonable weight, with a sharp, cut on contact broadhead, flying straight ( well tuned to your outfit) has plenty of "force" available to kill a whitetail or mule deer, the target of opportunity for most of us.

For smaller game, obviously the same holds true.  For very much larger game, well, questions remain and that is something you should consider for yourself when preparing for such a hunt.
ChuckC

[monterey]

Geez, I'm with Zradix on this one!

Your numbers just don't relate to your keystrokes.

[Nativestranger]

Originally posted by monterey:

Of course it matters!   :eek:  

Measure momentum or measure kinetic energy.  Velocity matters!

I dug through some stats of a test I did about this time last year.  I chronoed eight bows with two arrows.  One is a 520 grain the other a 650 grain.  Both cedar, both full length/same length, both fletched the same.  Out of eight bows here is the velocity differential that I got from these two arrows.  The average of four shots for each arrow.  The bows were all weighed on my scale and the scale checked for accuracy with a 45# weight.  the first velocity is for the 520 and the second for the 650.

bow one    28#  153-146 = 7
bow two    30#  139-131 = 5
bow three  34#  149-144 = 5
bow four   46#  164-156 = 8
bow five   44#  170-163 = 7
bow six    40#  163-154 = 9
bow seven  37#  153-146 = 7
bow eight  35#  165-157 = 8

I doubt if many bows will produce significantly different results, yet your test velocities were spread far beyond what is typical.

So, I then went to the range alongside my house with bow number six.  Selected because it is what I will shoot this year for hunting season and also because the two arrows tested below fly equally well from this bow.  Once again, these are POC shafts full/equal length, near identical fletch, identical poly finish on the shaft, both 11/32", one with a 190 grain head and the other with a 145 grain head.  Obviously, FOC will not be the same.  The shaft weights were 575 grain and 525 grain.  Fifty grains difference and with a rather low percentile difference since they are both fairly heavy arrows compared to the 300 an 400 you shot.

I shot seven shots with each into a new foam target that had had only five shots into it prior to this test.  None of the test shots came even close to any pre existing hole.

So, I measured and averaged the seven shots with each arrow.  They were shot alternately so that there was not a shooter fatigue problem or a creeping variation in shooting form.

Came up with this:

575 grain arrow average penetration 10.27"

525 grain arrow average penetration  9.71"

I suggest that you find a bow that will shoot both arrows equally well and do another penetration test.  I think your results will be different.  Or, you can send the arrows to me and I will sort through my cache of bows for one that shoots them equally well and do this same test.

So, season opens in less than two weeks and I just wasted a shooting session on this!       Gotta get back down to business.    [/b]

May I know what bows are bow #1 and #8? What is your drawlength? Those are very impressive figures.

[Nativestranger]

Your data for bow #1:

28# 650 grain 146 fps
(146 x 146 x 650) / 450240
Kinetic energy = 30.77 ft.lbs

Blacky Schwarz's controlled test data for 45# Bear super kodiak recurve:

44.5# 399 grain 186 fps KE= 30.28 ft.lbs

Good Lord your 28# bow shot with fingers produces more arrow energy than a 45# recurve bow shot with a shooting machine!
Even given a very optimistic efficiency figure of 80%, the bow's stored energy works out to be at least 38.46 ft.lbs. So it has over 1.37 Stored energy/ draw force value. That figure beats many compound bows drawn to 30"! Or maybe you have a 38" draw. Which is why I am curious how did you arrive at those figures. What was the bow used?

[TSHOOTER]

How is this related to Traditional Bowhunting?  Can someone explain to me what has happened to this site?

[The Whittler]

I can see where it relates to trad. hunting. It tells me that you don't have to shoot high poundage bows with very heavy arrows to get good penetration on certain animals.

[monterey]

First off, Let me clarify an error on my part.  This goes way back to when I originally tested these bows and the draw weights were summarised inch by inch for the sake of later creating FD curves.  In a hurry while typing the above post, I snatched the draw weight of Bow #1 from the wrong position. The correct draw weight at 28" is 34#.

All the draw weights listed are based on AMO standard of 26 1/4" measured at the deepest belly side of the grip.  My draw is pretty much 28".  However, my draw length, and anybodies for that matter, will vary depending on the design of the handle and grip.  For example, an ASL bow with a flat grip area is shot with the base of the thumb pressed into the handle.  This will usually cause a small loss of draw length compared to the pressure point being in the web of the thumb and the index finger.  

Irregardless, due to the depth or front to back thickness of the handles on the ASL type bows tested it is pretty much a wash since they tend to be deeper from the low point of the grip to the back of the bow.  IOW, depths in the range of 1.75" to 2" and in one case a bit more.

One of the bows, bow #2, is an osage self bow with only 1.25" depth in the grip.

With the exception of #2, all are wood/glass lam bows.

But, all in all, if one uses the common method of measuring the length of arrow actually drawn to the back of the bow, the draw lengths for all of these bows when drawn by me are right in the 28" range.

A somewhat lengthy explanation, but possibley pleasing to one of your profession.    

Bow #1 is a 1970 vintage Shakespeare Super Necedah 54" recurve.

Bow #2 is an osage self bow.

Bow #3 Is my own build, a 68" ASL with about 1/4" of string follow.

Bow #4 Is my own build, a 68" ASL with flat limbs and a 2" deep handle.

Bow #5 is a pre 70's vintage Howatt Cavalier 62" static recurve.

Bow #6 is my own build, a 66" ASL with flat limbs.

Bow #7 is a very odd little bow that you need to see and shoot to really appreciate.   It is a 1954 vintage bow with no name applied to it.  It has an aluminum handle, is ambidextrous, has limbs that are made of solid fiberglass, very narrow and conforms very much to an ELB in that it narrows from front to back and side to side with fairly narrow tips.  When you look at this bow the first thing that crosses your mind is "kid bow", but it is not!  This bow has taken big game.

Bow #8 is my own build, a 68" ASL with approximately 7/8" of reflex that is built in a continuous arc of a circle in the last 24" of the limb.

Bow #8 is impressive.  Funny thing is, when this bow was finished I did not like it at all.  Did not like anything about it!  It is however a very good performer.  Even at that, it does not fit my style very well and I cannot shoot it as accurately as most of the others.  The other great performer is the Howatt static recurve.  It too is a poor fit to my hand and form and not as accurate for me.

Just about the most pleasant to shoot of all eight is the osage self bow.  A good fit to my hand, smooth drawing and stack free out to 29".  I would hunt with it but it does not meet the minimum draw weight requirements for big game in Colorado.

[Nativestranger]

Thank you for the clarification. I did enjoy reading up on your bows used for the tests.
One thing to consider is this: your data do seem peculiar to me in that the velocity gain is very little when dropping arrow weight. Put it in another way the energy lost going to the lighter arrow seems quite a lot. Example bow #6 (which you tested for penetration) lost almost 12% kinetic energy going from 650g to 520g. Anyway your tests may simply conclude the same thing as mine. Less KE = less penetration. On my 40# bow going from 400g to 300g the KE lost is only 4.5% and there's no noticeable difference in penetration.

This test data of a 60" recurve is taken from Arctradionly. Very precise tests done with shooting machine. Notice going from 12 gpp to 9 gpp the speed increase is 25 fps. Notice that KE and efficiency stays more or less constant above 10 gpp. But drops marginally going to 7 gpp. This shows that my data are nothing out of the ordinary.
 

[WESTBROOK]

KE is a good indicator of energy at impact but not so much after impact.

KE v.s. momentum is a lot like HP v.s. torque.

Those snappy little motors that they somehow get 300+ Hp from have very little torque and are useless for towing and are constantly downshifting when going up hills.

Compared to a small diesel with perhaps less Hp but twice the torque might not be quite as quick but haul the load almost effortlessly .

KE/HP means you got a quick arrow but momentum/torque is what gets you out the other side.

[hybridbow hunter]

Bow #8 (35#)  shoots 520 gr arrow at 165 fps for 28" DL and 650 gr at 157 fps?
This means 165 fps for 14.86 gpp and 153 fps for 18.53 gpp at 28" DL out of a 68" American semi longbow design                  . Was it in  bow used in " the Avengers" movie?  
That's maybe the fastest trad bow on earth or maybe inaccurate #

[Nativestranger]

Bow #8 Stored energy/ peak draw weight works out to be min of 1.27 (assuming a very optimistic 80% max efficiency) a value not only beating Border's super recurve limbs but also many compound bows. Quite remarkable for any longbow.

[2bird]

Originally posted by hybridbow hunter:
Bow #8 (35#)  shoots 520 gr arrow at 165 fps for 28" DL and 650 gr at 157 fps?
This means 165 fps for 14.86 gpp and 153 fps for 18.53 gpp at 28" DL out of a 68" American semi longbow design                       . Was it in  bow used in " the Avengers" movie?  
That's maybe the fastest trad bow on earth or maybe inaccurate #

Yeah thats what i was thinking too. if you gave that bow 1/2 a fps for each grain of arrow weight it would be shooting a 10 GPP arrow 242 fps...

[monterey]

It was over a year ago that I did those numbers.  Last thing I want is to mislead anybody and would never intentionally present erroneous data.

I will pull bow 8 on the scale later today and will also double check the scale accuracy.  If my scale numbers are correct, I will reshoot the bow over the Chrony.