Gel vs water penetration?

[Chuck Whitlock]

A fluid has less resistance than a solid.

[tomjohnson]

And so less resistance results in more deformation of the bullet?

[DocGKR]

You are dealing with a fluid which flows and cannot resist shear forces, thus altering the hydrodynamic drag as velocity decays.

[tomjohnson]

Thanks, Doc. I was correct, in that I had a pretty good idea that the answer would involve concepts of physics far beyond my comprehension.

[Unobtanium]

You are dealing with a fluid which flows and cannot resist shear forces, thus altering the hydrodynamic drag as velocity decays.

Maybe why people die so damn ugly when they jump from a bridge that's high enough over water.

[DocGKR]

Exactly--jump from the same bridge with a parachute and the water does not feel so hard on impact...

[Jeep]

Of course, the solid land of a drop zone doesn't feel nearly as hard if your chute deploys than if it doesn't so that wouldn't seem to be something unique to a fluid.

[DocGKR]

Actually there is a dramatic difference....

[Jeep]

Actually there is a dramatic difference....

You'd need to explain that to me, Doc. I am by no means a physics guy--I don't know what a shear force is--but I am an old airborne guy. I've seen guys survive both land and water jumps when their main chutes collapsed, and I've seen the contrary result (at least on land jumps). But I'm probably missing something.

[QED]

Water generally reveals the maximum upset which can occur to a projectile in soft tissue--the actual expansion in living tissue will be somewhat less. Water testing also can be used to get a rough estimate of bullet penetration depth in soft tissue--bullets penetrate approximately 1.6 to 2 times as much in water as in soft tissue.

Considering the source, I am certain the above is true. Here is what I need help with, though. It seems as if upset and penetration should vary inversely. The more the bullet expands, the greater its frontal area, therefore the greater the drag, therefore reduced penetration. However this medium provides both more expansion and more penetration. How can this happen?

As a typical handgun JHP impacts water (at typical handgun velocities), it encounters just about as much drag as it would upon impact in 10% ordnance gel. The drag forces, however, become small or even negligible, in water or gel, as the bullet slows down.