Super-Bullets Slice Through Water (And Flesh)

A rifle bullet can go clean through a brick wall - but there's one sort of protection it can't deal with: water.

In the movies, a fleeing hero who dives into the water is invariably safe when the bad guys open fire on him. Mythbusters looked into this one, and after some elaborate tests with a range of weapons and ammunition, confirmed that water really is 'bulletproof' and rounds will either break apart completely or be effectively stopped within a few feet:

The surprising thing about the bulletproof water was how poorly the high-powered rifles did. The full metal jacket bullets for the high-powered rifles came apart upon hitting the water. Even the dreaded .50 caliber rifle was only able to penetrate about 3 ft of water.* *

But supercavitating bullets cut through water far more easily than normal projectiles, as I discussed I recently in a Wired News article. Perhaps more importantly, they can punch right through the air-water interface which defeats normal ammo. Blunt-tipped projectiles moving at high velocity will create a 'bubble' of low pressure around themselves and can pass through the air-water interface much more easily, retaining velocity into the water.

The Russian APS Underwater Assault Rifle fires long, flat-nosed projectiles- the pics here give you a good idea of what they look like and why the magazine is that peculiar shape. (Pedant note: the APS is actually a smoothbore and not a rifle at all.) According to the makers, it not only has a range of up to 100 feet underwater, it can also be used to fire from the air into the water. The weapon could be used to shoot at divers or swimmers from a boat, for example - or even fire from underwater into the air. In theory, a squad of APS-armed Spetsnaz frogmen could carry out an ambush on a convoy passing over a bridge from underwater, while being immune to return fire… but I can see some problems with this concept.

More practically, the cavitation effect is used in the Venom Penetrator darts being developed by the U.S. Navy. A mass of these darts dropped in the surf zone would neutralize mines in sand as well as those under several feet of water.

Even more ambitious is the RAMICS program, another anti-mine effort. The helicopter-mounted 20mm cannon could destroy mines within 20 feet of the surface with a special supercavitating projectile. This has now been upgraded to 30mm, but initial operational capability is not expected until 2010 or so.

Another related idea is how well a supercavitating round will go through flesh. The supercavitating SuperPenetrator is a special Big Game bullet designed by Norbet Hansen for maximum penetration. He tested the round on elephantsand found it 'extremely effective' compared to other bullets which can tumble or break up and fail to kill large animals cleanly. Earlier I was dubious about where you really could take on a shark with an underwater gun, but maybe the makers are correct when they claim the APScan defend against ' rapacious fish', and ' even shark.'

(Many thanks to Max Popenker of world.guns.rufor the APS photo)

P.S. The idea actually goes way back. As Nathan Okun points out, the Japanese used this principle in WWII for shells intended to hit ships below the waterline. Luckily they didn't work too well.