There are two versions that feature a compact barrel, the CAR-15 as a general term refers to the name Colt gave the AR-15 in an attempt to re-associate the rifle with Colt, hence Colt AR-15.
Are we are still talking about high powered rifles here, or did we switch to BB guns? The velocity of these rounds is still extremely high. If a 5.56mm round can puncture steel, it can sure as hell go straight through human tissue. If the round regularly split apart and caused multiple internal injuries, NATO wouldn't allow it.
Chances are if you're stuck in the field for a few days, you're more apt to take the weapons of the soldiers you've killed instead of reloading your own with the few spare rounds you stuck in your pocket. The bullet sizes aren't even that much different. You might be able to fit one or two more 5.56 in your pocket than 7.62.
The gun isn't yours, and you clearly haven't done any research. The fact that your family is full of gun-toting hillbillies doesn't mean you know stuff about the rifles they own. You seem to think you know exactly what's going to happen when you shoot somebody, but you're not even old enough to enlist.