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|
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.