Ptrs rifles should work, you just need to know where to hit. Avoid hitting vehicles on frontal areas (where armor is much thicker) and try to hit in the rear or the side of a vehicle. Also keep in mind, that the further away you are from a target, the less penetration.
To turn off those messages, you need to alter your game files, and if you arent used to these things, I wouldnt recommend it. If you really do loath them, you could download the mod "Dynamic Campaign Generator" (
http://www.moddb.com/mods/dynamic-ca...-generator-dcg) which has the necessary fixes done (but using mods do alter the game experience and can make the original missions very un-balanced).
~Zeke.