Tar? Seriously? In my experience, the bullets being pushed into the case is more of a mag issue than an issue with the ammo.
Some people have experienced popped primers and some have reported issues with key-holing with the Norinco 223 ammo but in the several thousand if shot I've never seen either of these problems. The primers are apparently hard and not much fun for bolt guns but for semis, it's good cheap fun in a can! For those inclined, the primers pockets are not crimped which makes for easier reloading.