The past few years penetration testing has become a hot topic. As bows have begun to top out in speed (The Fastest Bow Possible) more attention is being paid to other ways of optimizing archery equipment. Of course penetration has always been of special concern to hunters so as to cleanly kill our game as quickly as possible.
Archery Report has covered penetration using multiple methods, see Arrow Penetration Testing: Real Bows, Real Arrows, Real Results. We’ve also talked about the theory of penetration in animals vs. in foam targets: Friction and Penetration in Archery: target vs. animal penetration. This article is going to take a closer look at penetration in foam with real world testing.
Test equipment and setup
This test will be conducted with the same two arrows used in the Arrow Penetration Testing: Real Bows, Real Arrows, Real Results. These are Victory HV arrows, both with identical outside characteristics and points, though one is layered inside with another shaft and point. They weigth 300 and 561 grains and have nearly identical front of centers. This time I’ll be using a Hoyt Ultratec set at 50 lbs. and a 28.5″ draw length. I attempted testing with a higher draw weight and my normal 30″ draw, but the arrows penetrated too much for reliable testing (I need denser foam!)
The test media is ten layers of a dense, virgin packing foam. All shots were to previous untouched areas to ensure that previous shot holes did not affect the penetration. Shots were at a distance of 10 yards from the target. Each round the heavier and lighter arrow were both shot, measured and removed for the next round.
Arrow penetration results
The data speaks for itself:
| 300 grains | 581 grains | |
| 1 | 26.250 | 25.750 |
| 2 | 26.625 | 25.875 |
| 3 | 26.375 | 25.500 |
| 4 | 26.000 | 26.125 |
| 5 | 26.875 | 25.750 |
| 6 | 26.125 | 26.125 |
| 7 | 26.250 | 25.875 |
| 8 | 26.125 | 26.250 |
| 9 | 26.376 | 25.750 |
| 10 | 26.500 | 25.625 |
| Average | 26.350 | 25.863 |
Both arrows were very close overall, but when taking the average the lighter arrow out-penetrated the heavier by just under 2%. So how can this be? How can this have the opposite result of all the other testing? If you’ve read the Friction and Penetration in Archery: target vs. animal penetration article you’ll know the answer.
The physics behind penetration in animals and other media the does not immediately collapse on itself with a rebounding force is different then a spongy, dense foam that can collapse on itself in a rapid manner. My theory from the previous article seems to hold true with this testing: as the foam collapses, it puts pressure on the sides of the arrow and thus friction on the arrow shaft, slowing it down. The lighter arrow has the advantage of moving through the foam faster than the heavier arrow, thus giving the foam less time to react and collapse around it. This is still my “theory” as I have not figured out a way to definitively prove this, but the theory seems sound and the testing backs it up.
So what does this mean? It means that while many people will try to test penetration in their foam targets, the results they see have a strong likelihood of not being valid for comparing penetration in hunting situations. I like to see people getting out and doing testing, however, many times this testing when done without a full understanding of what is going on can lead to a lot of misinformation and urban myths being propagated.
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{ 10 comments… read them below or add one }
Couldn’t you use ballistic gel instead of foam and also shoot with a much weaker bow to ensure that the arrows don’t pass through?
Ballistic gel is great stuff, but it also has it’s own issues. First, it’s expensive to make in quantities necessary to get a statistically valid number of shots into. Also, it’s difficult to make it consistently and it changes with temperature, humidity etc. It’s also affected by gravity, so shooting into a higher spot may have a different result than shooting it into a lower spot.
I am looking into making a few variations of gel and doing some testing with it in the future.
Make your own. It doesn’t have to be 100% FBI calibrated, just a consistent mix. Shoot into it, recycle, then shoot into it again until you have a nice sample size.
http://www.firearmstactical.com/tacticalbriefs/volume3/number2/article1.htm
I forgot to start with: Nice job you all are doing. Love the site and the information you provide!
Try this recipe http://youtu.be/ZRkDZd7FgDg, seems like a good tutorial. I think that this would be your best medium to shoot through.
He gives a good tip on how to save money when making the gel in large quantaties after ca 50 seconds into the video.
Excellent info that video Christopher. Thanks, I’ll look into it.
What about sand? I know it is not a very good representation of say an animal but I would think a reasonable tamping down of the material after every shot should give you statistical consistency. It would also likely five you a decent measure of the energy of the arrow?
Pat, I’ve considered sand in a 5 gallon, square sided bucket and it does have some possibility. The biggest issue, as you noted, is that it will behave quite a bit differently an animal body. Through enough testing it may be possible to show if there is a good correlation or not, and it’s very re-usable.
All in all this is an ok test.
I have a problem with your theory about the foam collapsing.
Although see if a speed variable friction coefficient works for foam/CF.
Friction behaves very weird at different speeds, it is not the constant force we learn about.