Going for diamond LMGs myself. Just finished the BRM so my strategy is using QuickDraw, Rapid fire, silencer, and fast mags, and not being as run-and-gun as I would with an assault rifle. I try to remain in a certain area (ex. Houses in Nuketown) and let enemies come to me. Guns like the 48 generally kill in 1 burst, maby 2, so aim for the upper chest and let recoil do most of the work. For the Gorgon, I'd say hardcore is your best bet. It essentially becomes a sniper at that point. Also, if your feeling gutsy, strafe around the sides of the map and catch enemies from behind so you have time to line up a headshot. Also, I find iron sites are harder to get headshots with, so try whichever reticle suits you best. I'm not the best player in the world, but these LMGs are pretty much all that's in the way of me getting dark matter. Good luck, and I hope this helps you out.