I have no idea about the differences in tolerances and reliability between “army grade” and “consumer grade” weapons, but I know that the MG3 is renowned for being extremely reliable in military context.

I’ve never even thought about trying a bump stock, but the idea that some of the energy that “should” be going into properly chambering the round instead goes to simulating automating fire, and that it therefore increases the risk of a misfeed or jam makes a lot of sense.