[quote=@MelonHead]
<Snipped quote by Rain>

Rock-skin is basically the bane of all firearms, depending on its thickness, so you're basically shit out of luck regardless. However, I do know that a lot of assault rifles incorporate under-barrel grenade launchers, that would be a must for one inclusive weapon. 
[/quote]

Not necessarily. Again depending on the thickness a battle rifle (Large caliber select fire weapon) can eat away at it something fierce. Ammunition is a large factor into the effectiveness. Velocities, weights, distances. Lots can be factored in.