Thread: terminal ballistics penetration.

a simple mind experiment.
say you have 2 penetrators of equal diameter made of the same material, but differing length(and naturally weight)
each of them are shot with exactly the same energy.
according to newton, these rounds should exert exactly the same amount of energy onto the surface,
but will the longer penetrator penetrate deeper?
oh, and please try and ignore any fuss over long penetrators wobbling, air drag and all those nice things, that are external ballistics.
i'm only interested in the terminal ballistics effects.

I don't know a lot of physics, but I can't imagine why length would make a difference. Assuming the force of impact, and the shape and width of the rods is the same, i'd assume penetration would be the same.

If they are of equal kinetic energy, the shorter, lighter projectile will be going faster than the longer, heavier projectile. The longer, heavier projectile will have more momentum.

Ignoring such factors as mushrooming of the bullet, the lighter, faster projectile will expend more of its energy in the hydrostatic shock wave that propagates through the target on impact. The long, heavy bullet will use its KE to penetrate deeper.

If we are talking about a solid target, then the heavier bullet still wins because of its greater momentum. This is why depleted uranium is good for penetrating tank armor.

Originally Posted by Harold14370

If they are of equal kinetic energy, the shorter, lighter projectile will be going faster than the longer, heavier projectile. The longer, heavier projectile will have more momentum.

Ignoring such factors as mushrooming of the bullet, the lighter, faster projectile will expend more of its energy in the hydrostatic shock wave that propagates through the target on impact. The long, heavy bullet will use its KE to penetrate deeper.

If we are talking about a solid target, then the heavier bullet still wins because of its greater momentum. This is why depleted uranium is good for penetrating tank armor.

What you are saying is demonstrable. And rings true.


However over the years when doing ballistic testing. I found that large rounds not going fast enough, would spatter on a sheet of metal. While a much smaller faster round effortlessly penetrated the safe.

The heavy round created a sound similar to the safe being hit with a ball peen hammer. But did not even chip the paint.

That same round fired out of a longer gun with a larger load could penetrate the safe very nicely.

Just offering some other view points.

Sincerely,


William McCormick

Originally Posted by dejawolf

a simple mind experiment.
say you have 2 penetrators of equal diameter made of the same material, but differing length(and naturally weight)
each of them are shot with exactly the same energy.
according to newton, these rounds should exert exactly the same amount of energy onto the surface,
but will the longer penetrator penetrate deeper?
oh, and please try and ignore any fuss over long penetrators wobbling, air drag and all those nice things, that are external ballistics.
i'm only interested in the terminal ballistics effects.

Penetration mechanics is quite complicated. Penetration is highly dependent on the material properties of the penetrator the object to be penetrated the geometry of both in addition to energy and momentum.

The physics of the penetration event are quite involved, and it is not as simple as just length or just velocity or just momentum or just energy. A very long rod can break up on impact, basically due to bending and Euler buckling. But high sectional density is also helpful and comes with length. Strength of the penetrator is also very important.

There is no simple answer to your question. When tank penetrators, for instance, are designed, the process involves use of sophisticated penetration mechanics computer codes on high-end computers, specialized physics knowledge. Even then no one believes the results until after full-scale tests are conducted. There is a significant amount of intuition and experience that goes into the definition of the designs that reach the testing stage.

Tank penetrators are often made of depleted uranium. One reason is that DU is very dense and therefore has high sectional density, a lot of momentum with minimal drag. It is a good penetrator. Probably the more important reason is that uranium is pyrophoric -- after penetration the bits of spalled uranium auto-ignite and create lethal fire.

If you are talking about sporting ammunition, then generally deep penetration is obtained with heavy projectiles at moderate velocities. The heavy projectiles provide high momentum to keep things going in a straight line and the moderate velocity avoids driving the bullet so hard that it breaks up. For the deepest penetration full-jacketed ammunition with reinforced tips is used. The most important issue for deep penetration in this context is for the bullet to hang together and not break up. Mass retention is the key.