Working on Diamond LMG's currently, and I have used the LSAT almost exclusively. I have to ask though, which of the LMG's is the "hardest" to get Golden? I know they're all pretty high damaging but I haven't used the MK48, QBB or HAMR so I don't know how all of them perform at range.
"You must be the change you wish to see in the world" - Gandhi
Definitely the QBB. Nothing it is good at is good for getting camos - the recoil is the worst of the LMGs (to the point where LONGSHOTS are a pain as well) and it has a terrible headshot damage multiplier.
I just Diamonded the LMG's. QBB LSW was actually my best LMG for headshots. Mainly I played HC KC and farmed for headshots or played Core and aimed for likely head glitchers. My K/D is lower than the others, because I focused on just getting the headshots. It was, though, the one gun I was happy to get done with. I used the HAMR next, and breezed through it although it took me a bit longer for the headshots.