expanded diameter

[Disciple]

Doc, you wrote:


While on a casual first glance, both the Corbon DPX and Federal HST could initially appear to have larger expansion, the actual measurements demonstrate that all the recovered .40 S&W projectiles in the photo above, in fact all have exactly the same RD of 0.64". Also, be mindful that RD measurements are made at the leading edge of the projectile, not further back down the expanded "petals", as this can give a false reading. For example, in the photo above, when measured half-way down the expanded projectile, the widest part of the expanded "petal" measures 0.84", much larger than the calculated RD of 0.64".

Why are the smaller numbers used for analysis? A broad head arrow tip would appear little more effective than a target tip if average diameter is used, but that is clearly not the case. Is the interaction of bullets with living tissue so different from arrow tips that this analogy is meaningless?

http://www.alaskabowhunting.com/images/Product_Photos/Broadheads/broadhead-3.jpg

[DocGKR]

At the velocity a broad head arrow is traveling at, as well as given its "broad" shape, those nice long edges are efficiently cutting a significant amount of tissue vs. a target arrow that is just poking a small hole.

[Disciple]

Doc, that is precisely my point. Let me rephrase my question: is this "broad head effect" not present in the case of something like the Barnes XPB bullet? Are the "petals" simply not sharp enough to work this way?

[Marcus L.]

If you ever do any hunting you can observe the dramatic difference between a target arrow and a broad head. After you've cut open the animal, you can see just how minimal the damage is to the tissues the target arrow penetrates. Except for a small crush hole about half the diameter(maybe 2-3mm) of the target point, the arrow just pushes the surrounding tissue and arteries aside. In order for a target arrow to be effective you really need to take out both lungs or the heart with such a small crush cavity.

You can get the same effect with different shaped handgun bullets. If you use a full wadcutter bullet(flat point that extends the entire diameter of the bullet), there is virtually no tissue pushed aside and the bullet makes almost a 100% crush cavity for that bullet diameter. A sharper point can result in less crush cavity and more tissue pushed aside depending on the bullet velocity.

Here's a little hands-on test to understand this. Get yourself a pine 2x4, a hammer, and two sharp nails. Use the hammer to flatten the point of one of the nails just enough to give it a semi waddcutter profile. Hammer the sharp nail into the 2x4 two inches from the end of it.....the board will split around the nail because the material is being pushed around the nail. Now hammer the flattened nail into the 2x4 two inches from the end.....the board will not split because the material is being crushed as the nail penetrates.....not pushed around the nail. Old carpenter's trick.

With the low velocity and momentum of a target arrow, you cannot use a wadcutter, semiwadcutter, or expanding point and have any penetration......so you must use a broad head with cutting blades. With handgun velocities and momentum, you can use these blunted projectiles and have very good penetration and any tissue in the path of the bullet is destroyed with a minimal amount being pushed aside. This is why the outter diameter AND inner diameter of the expanded bullet are important considerations when calculating your wound volume. The shaft of the broad head does not have the velocity or the flattened head to cause any significant crushing. The blades do all the work which is entirely cutting in nature.....no crushing and tearing which is what a bullet does.