Here’s a fun excerpt from a TV program showing how water, so much more dense than air, can slow down a bullet.
I used to think that the stories of divers attacking harbors, and swimming safely underneath a hail of bullets fired by sentries on shore, were just that – stories. However, way back when, I saw some South African divers training at Walvis Bay prior to an operation in Angola. Part of the training was to show them that sufficient depth of water (about 3 meters, or 10 feet) would, indeed, protect them from AK-47 fire. Sure enough, as they swam along next to the quay, their instructor fired an AK-47 at them, and the bullets were slowed to a crawl before they could reach the swimmers. It was very educational.
(Note to readers: DON’T try that at home – or anywhere else!)
Peter
Mythbusters did a show on this, too.
Yep. See: https://www.youtube.com/watch?v=yvSTuLIjRm8
Fired everything up to and including a .50 Cal into a pool. They were ready to pack up and leave quickly in case they put a hole into the bottom of the pool.
The rifle bullets didn't travel as far as the pistol bullets as they tended to break up more quickly.
Brass
IIRC, a bit over 1 m of water slows down 7.92×57 mm Mauser FMJ enough that it won't penetrate a body, unless you're unlucky enough to take it the eye or something.
The spin rate of the bullets also contributes to the slow down/break up of the bullet. An arrow however, WILL penetrate 10 feet of water easily, due to the lack of spin.
Old NFO:
I would think part of it would be the high mass to frontal area that allows those arrows to travel so far in water. Spearguns, essentially.
Pistol bullets seem to be the most dangerous in water, as they travel farther than rifle founds do. High velocity seems to be a restricting factor.
I was going to point out the Mythbusters episode too. The SPLASH as that 50cal round hit the water was impressive, and it didn't penetrate the ballistics gel only a couple feet underwater.
Darn…Wish I'd read all the way through your post to the disclaimer at the end. Now I'm banned from the YMCA pool.
Sure did give them old fellas doing the freestyle laps something to remember though.
I had a conversation with a friend/instructor concerning home defense. When I cited ducking behind the bed, he pointed out that a bed is not hard cover, but simply concealment. I refuted his point by citing that I sleep on a queen size water bed, which is indeed hard cover.