The Physics of Russian Bog Cartridge Pucker

[jeff w]

I've noticed that when they pull a T-34 from a bog or river the cartridge cases get puckered up. I'm not a physics major - anybody know what causes this? My guess would be something is leaching out and causing a vacuum. Or can 70 years/temperature/pressure alone do this to the brass?

 

[glevum]

What was the depth of water?

It looks like pressure damage to me. The pressure increases by 1 bar every 10m.

15psi every 30 feet in imperial units

 

[Nabob]

I imagine more pressure, something like a handgrenade in floded compartment of the tank.
Bob

 

[Michel]

It's pressure damage like Glevum already wrote. On shipwrecks a lot of the complete shot looks like this. The ones that are straight and look good are stronger or where not as water/pressure thight sealed so the water could get in quickly.
The other way around is also possible so if complete shot comes up from 40 meters of water, on the inside of the cartridge is a pressure of 4 bar that wants out. I think this is due to the fact that the pressure inside equalized over a long time to seabed conditions and if someone brings it to the surface in a short time there could be a nasty surprise waiting.