It wasn't 1atm of pressure. The round passing through the (enclosed) compartment of the target at high velocity created a vacuum that sucked any soft material out after it. There was also the explosion that happened on the armor, and some sort of plasma that went in after the round that all probably contributed to the effect.

I don't know the technical details, and as I said, they were pretty proprietary with exactly how the thing worked; I was just a grunt assigned to carry out around and fire it. We had some Swedish military guys training us and consulting on the trials, and that's what they told us the effects were. I assume they'd tested the thing with pigs or something; I don't know if it was designed that way or just a happy side-effect.

What I remember most is that it was like playing a video game, and that it really fucked up tanks. We got to look at the results, and while our targets didn't have any animals in them, it did seem to incinerate anything that wasn't bolted down and spray it on the ground under the target.

The wiki article is equally tight-lipped about the exact mechanism of action. I just know it was different from a TOW in that the damage wasn't from a warhead exploding against armor; it was firing a projectile via a shaped charge as it passed over the target. There was much more debris left of the missile than we found from TOWs, although it was still a pretty destructive process for the missile.