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One of the most controversial subjects in archery is what type of arrow penetrates the best.  Discussions revolve around arrow diameter, broadhead type, front of center (FOC), arrow weight, etc.  This article will focus on the most controversial of the variables, the arrow weight.  You can hardly visit an archery related message board without finding at least a few posts on this subject that range from new archers asking questions to all-out mudslinging debates on who is right.

I have long been a fan of such debates as the subject delves deep into archery physics with all sorts of theory and equations to go along with it.  This site already contains a few related articles such as Heavy vs. Light Arrows: Downrange Speed and Power and Arrow Kinetic Energy and Momentum but this particular article is going to focus on real world testing.  The other articles are full of equations and physics musings and are great background readers, so don’t miss reading them.

The testing I plan is going to take place over several months, maybe even longer as I delve into it.  As things progress, I will continue to update everything here.  I also welcome any insights, ideas or experiences you may have to share.  If you have solid data collected in a quality manner, I’d love to see that as well.

To start things off, I am beginning with developing multiple ways to test penetration.  Anecdotal information from real animals shot is always great, but its biggest problem is that there is no control over the variables.  Shooting animal corpses and body parts repeatedly to gain a full data set is better, yet still very difficult to control the continuity between each shot.

For some initial testing to determine a good way to do long term testing, I am beginning with the humble milk jug.  While not nearly a perfect substitute for a deer, elk or boar, the milk jug has a stiff outer shell, liquid center, followed by another shell.  The idea is similar to an animal, easy to obtain, consistent and at least a decent place to start playing with ideas for further testing.

The next important item needed is a group of control arrows.  For initial test development, I will be using Victory VForce HV arrows.  I chose these shafts because I am able to get a very light arrow, along with a fairly heavy arrow by layering a 1516 aluminum arrow inside of the carbon shaft.  By using the same exact outside dimensions for both the heavy and light arrows, all elements of the test relying on the physical phenomena of the arrow touching and passing through any test medium is held constant.  Also, I am able to add weight to the front of the heavier arrow through different screw in points as well as weight inside the inserted aluminum shaft in order to get close to identical FOCs on each arrow.

Initial test equipment

  • Bow: Elite Envy, 29.5″ draw length, 60 lbs. draw weight
  • Rest: Limb Driver
  • Arrows:  Victory VForce HV
Test arrows including FOBs used in Part II

Test arrows including FOBs used in Part II

The light arrows weigh right in at 300 grains, the heavy arrows at 561 grains.  The FOC on the light arrow is 11.80%, the heavy 11.75%.  Both arrows have been tested and tuned to the bow to shoot correctly.  Neither arrow has any fletchings as the milk jugs tear them off after a few shots.  All shooting is done at close range for initial testing.

Arrow penetration test initial setup

Both arrow types will be shot through an Easton Pro chronograph at six feet distance.  After the normal speed of both arrows is determined, the arrows will be shot through a water filled milk jug at six feet, with the chronograph placed four feet behind the jug.  This will give the velocity of the arrow after passing through the jug.  All results will be the average of a minimum of seven shots, with the highest and lowest results thrown out.

Test arrows with identically front profiles, one heavier than other to balance the FOC

Test arrows with identical front profiles, one heavier than other to balance the FOC

By knowing the initial velocity and the velocity of the pass through, the amount of energy expended during the pass through and the remaining energy of the arrow can be determined.  This will help to benchmark which arrow is more efficient at penetrating the jugs.  All shots will be at the lower portion of the jugs where the distance between the front and back side is consistent and the walls are parallel to each other.

First pass results

The initial speeds of the arrows were 324.5 fps and 243.6 fps for the light and heavy arrows respectively.  All shots of the bare arrow were within +-0.3 fps.

FOC marks on bow arrows with tips lined up

FOC marks on both arrows with tips lined up

The results of shooting through the filled gallon jugs were 245.2 fps and 199.1 fps.  These shots had a variance of +-2.4 fps, which is to be expected since there are more variables including precise thickness of the jug at the points of contact, angle of contact, variations in plastic density, etc.  I was pleasantly surprised that the results did not vary more.  While far from perfect, it gives me a good idea of where this testing is headed.

To summarize the velocities, kinetic energy, momentum and the losses:

300 Grains 561 Grains
Initial Velocity 324.5 243.6
After Penetration Velocity 245.2 199.1
Initial Momentum 0.43189 0.60629
After Penetration Momentum 0.32635 0.49554
Initial KE 70.0755 73.8471
After Penetration KE 40.0108 49.3311
Retained Momentum 75.56% 81.73%
Retained KE 57.10% 66.80%

As can be seen by the results, the heavier arrow began with more momentum and KE, which is consistent with all of my other testing.  This is because as arrow weight increases, so does the efficiency of the bow and thus more of the stored potential energy at full draw is converted into the kinetic energy of the arrow at release.

What is most interesting is that the heavier arrow maintained over 6% more momentum and over 9% more kinetic energy after passing through the test jugs.  This is in harmony with my theory and with the governing physics principles.

Initial conclusions and next steps

This first round of testing does show that heavier arrows not only begin with more momentum and KE, they also have more penetration potential and retain a higher percentage of their initial energy after penetrating.  While these first results are far from a full scientific study and the total number of data points needs to be significantly increased, the data was quite consistent and shows that this test methodology may be worth continued use.  However, I’m going to need a lot more jugs!

Testing in the future will continue with a larger variety of arrow weights and tests that include bringing the arrow to a full stop.  I have some other ideas for test media that need to be worked out as well to provide a fully rounded approach to the testing.  Any and all ideas and suggestions are welcome!

Bonus Material

Here is my post on Archery Talk about this testing; some interesting conversation to say the least!
http://www.archerytalk.com/vb/showthread.php?t=1450085

Jugs line up in front of target

Jugs lined up in front of target

Penetration Testing Part II

While the first section dealt with penetration through one jug and measuring the exit velocity, this part takes a look at shooting through six jugs and what it takes to stop the arrows.

The equipment for this round is identical as the first, with the exception that I added a FOB as the fletching. I had first started with fletchings, but they were ripped off fairly quickly. For round one I removed the fletchings to avoid inconsistencies in fletching contact, but decided to go with the FOBS for round two because the arrows fly better with them. Both FOBs took virtually no force to come off the back end of the arrow.

 

Chronograph speeds of both arrows

Chronograph speeds of both arrows

Before doing penetration testing, I adjusted both arrows to have nearly identical FOCs with the FOBs. The final weights were 322 and 579 grains. Next I checked how they both tuned through paper. With nearly perfect bullet holes in paper, I was ready to get some speeds using the chronograph.

Five shots with both arrows were fired to check the speed and all shots were very consistent, within +/- .1 FPS. The lighter arrow averaged 318.9 fps and the heavier 242.3 fps. Summarizing the weights, speeds, kinetic energy and momentum:

322 Grains 579 Grains
Initial Velocity 318.9 242.3
Initial Momentum 0.456 0.622
Initial KE 72.62 75.41
Penetration of the 322 grain arrow

Penetration of the 322 grain arrow

With all the initial setup and testing out of the way, it was time to do some shooting and make a mess! I had twenty-four jugs saved up for testing, all of them from the same manufacturer and identical in every way. This gave me enough for two shots through six jugs for each arrow. All shots where taken from 5 yards away as this gave me enough room to kneel and line up the jugs as perfectly as possible (and to have the camera at the side in a good position.) Each of the two shots for each arrow had nearly identical results, so I feel they are valid so far as this type of testing is concerned.

The 322 grain arrow was first. As can be seen in the picture, the arrow was stopped by the jugs with about 1 1/4″ protruding from the first shot and 1 3/4″ from the second shot. As can be seen, I shot the jugs near the bottom of the flat section because that was the most consistent part of the plastic.

Pentration of the 579 grain arrow into target behind

Penetration of the 579 grain arrow into target behind

Next up was the 579 grain arrow. Both shots resulted in the arrow penetrating all of the jugs and ending up about six to eight inches into the target behind.

The heavier arrow performed significantly better in penetration and I’m not certain even seven jugs would have stopped it. I’ll save up some more and will repeat the test with eight jugs in the future. That’s a lot of milk, but I think my family is up to it!

Obersvations

As expected, the heavier arrow performed significantly better in penetration through a combination of fluid and solid media. The testing in this case was highly dominated by the fluid and as described in the Heavy vs. Light Arrows: Downrange Speed and Power article, faster objects will always experience a higher deceleration force than slower objects, all else being equal. Also, it’s important to note that the heavier arrow in both Parts I and II had significantly more kinetic energy and momentum.

More testing to come!

Anecdotal addendum:  the phone book test

Disclaimer: the following pictures are not indicative of a controlled scientific experiment, but rather a “fun” test that others have done and I wanted to have a comparison to their results. Shown is the penetration of the test arrows into and through two phone books. Notice the consistency of the heavier arrow out-penetrating the lighter arrow. Each set of shots was done on the same horizontal plane of the phone book, however the third set of shots shows how badly the phone books had deteriorated (though the comparative results are nearly the same.)

You can tell which is the heavier arrow by looking at the field point; the heavier has a slightly longer section behind the identical point section.

I emphasize:  this is not a good test to show penetration into animals.  It is a simple comparison and a common test shown by others doing penetration testing and I wanted to try it myself to see the results.

Phone book shot 1

Phone book shot 1

Phone book shot 2

Phone book shot 2

Phone book shot 3

Phone book shot 3


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