Mythbusters

[K.I.L.E.R]

They used guns to fire into water and penetrate ballistics gel.
Lower calibre rounds had some penetration but high calibre rounds from M1 Garand and a 0.50 calibre rifle with armor piercing rounds had the metal stripped off them in 3ft-4ft of water.

Why do lower calibre rounds have better penetration in water?

 

[YeuEmMaiMai]

They used guns to fire into water and penetrate ballistics gel.
Lower calibre rounds had some penetration but high calibre rounds from M1 Garand and a 0.50 calibre rifle with armor piercing rounds had the metal stripped off them in 3ft-4ft of water.

Why do lower calibre rounds have better penetration in water?

maybe due to less surface area or the speed of the projectile.

 

[Basic]

This is just a guess from someone who have pretty much no experience with firearms.
(I'm sorry if my terminology is all wrong.)

I haven't seen the program, but a friend mentioned it. He said that high speed weapons was stoped, while low speed had good penetration. (Speed as in bullet velocity, not in rounds per second.)
Bullets tend to fragment as they hit something solid.
With higher bullet speeds, the water will seem more solid.

So the high speed bullets fragmented early, and then they stop quickly.

 

[K.I.L.E.R]

That was what I initially thought but I don't think that factor alone could do it.
It really doesn't make much sense.

 

[Killer-Kris]

My initial thought was that it might have more to do with the angle the round hits the water. They tested the handguns and shotgun perpendicular to the water, and the rifles all at an angle. I would have liked to see them try the handguns at an angle and the rifles verticle as well, just to rule that out.

 

[{Sniping}Waste]

Bullet velocity has every thing to do with this. At higher velocity, the bullet has stored more energy on impact that will cause the bullet to go to pices. A bullet with less velocity will hold together better on impact and will travel farther from impact to a point. That is why the old springfield with a mini ball traveled farther in water then any other small arm. The springfield used black powder and not qardit and balck powder burns slower and produced less gas pressur that gives less bullet velocity then the newer small arms.

 

[idiom]

I heard it might have something to do with when the bullet goes supersonic it creates a pressure wave at the front and doesn't act nice when it hits water.

 

[the maddman]

Pretty simple, for a object to travel at supersonic speeds, it has to compress the fluid in front of it. Gasses compress, liquids don't. Supersonic rounds, on hitting water are almost instantly decelerated to subsonic speeds, and all that force heats and tears apart the round.

So, if you need to shoot someone swimming, I'd think your best bet would be a small caliber sub-machine gun with solid rounds. Like the H&K MP40 I get to play with

The rumored Russin SuperSonic Torpedo was supposed to travel in a pocket of water vapour, but who knows if that's real or not.

 

[the maddman]

Russin

Make that "Russian"

 

[silence]

The rumored Russin SuperSonic Torpedo was supposed to travel in a pocket of water vapour, but who knows if that's real or not.

its real

http://www.newsmax.com/archives/articles/2001/4/23/220813.shtml

 

[blakjedi]

cavitation is a well known principle in us naval circles... but i dont think its made it to any weapons systems yet...