Jim choate says:
The pieces in most cases are simply slivers of metal that breaks off the inside of the tank because of hyper-sonic shockwaves. They are not molten and do not in general cause a fire. Other than a lucky hit on a live round with the ammo door open there is little chance of starting a fire.
Actually, my last comment was premature -- I hadn't read what you said carefully. If you meant to say that such things as discarding sabot shots don't penetrate the armor directly, according to the Illustrated Encyclopedia of Ammunition, non-shaped charge armor piercing projectiles do indeed pierce the armor. Incidently, I was wrong on one point -- there is a kind of shell called a "piercing shell" designed to explode after penetration -- but these are apparently not very successful with modern armor and are rarely used. Perry PS again, this really should be terminated -- it doesn't belong in cypherpunks.