If they have incendiary rounds, possibly. It just matters of their caliber, too.
HEAP rounds silly. Given that no anti-tank rifles (.55 Boyes forget yes) are in service any more, the LAW (Lightweight Antitank Weapon) pretty much covers the entire job of destroying a tank with only small arms and no sneaky explosives magic.
One of the weakest bullets STILL used on the battlefield is the 5.56 caliber, But it still can shoot through a quarter-inch of steel. On blockland, that size bullet would do around 10-20 damage.
Define "weak", a 5.56x45mm NATO round is still bigger than the russian 5.45x39mm round, and delivers more impact energy. It certainly kicks more ass than FN's 5.7mm and H&K's 4.8mm.
how can I find out the position where the bullet would come out again?[/i]
If a projectile is inside a terrain, it should collide on the surface, raycasts certainly do though projectiles are questionable. In any case, if it does collide then you have a perfect moment to gather the projectile's transform.