You know, about the "path of least resistance" thing, you have to realize that a bullet rarely travels straight through a body. This is especially true of smaller caliber rounds. When a bullet enters the body, it encounters all manner of different densities which alter its path of travel. The bullet can "bounce" around inside of a person and create all kinds of havoc. Now, the larger the caliber and the faster the round, the less the bullet is likely to bounce, but you will almost always have a bit of deflection. Now when you talk about the rib cage, armor, and the tank itself, you have to think that there will be no straight line path for the escaping gas to pass out of. So the gas will force its way out through the general path of the bullet, but in doing so will distort the path greatly because of the gas' pressurized state. It would be like putting a piece of cooked noodle, surrounded by Jell-O, and coated in a few layers limp lettuce onto the end of a balloon-blowing-up helium tank and watching it freak out and wiggle when you pressurize it. Since the piece of tech in question is pressurize, you get the really nasty failure, not because it has failed, but because of the WAY it has to fail. And pressure valves will only dump product when the pressure gets too high, not when it starts to rapidly dump. OF course, I'm sure you could design one for that purpose, but it's not going to help when the gas is escaping through a hole that the valve doesn't regulate.
Gabriel