Any ar15 grip will fit, but like you said, on .308's there are some socalled gaps. Magpul fixed there MIAD gap problem and came up with a filler piece. There is another item in Brownells that is made to move your hand back a bit to get a better trigger finger position. It makes the fit better with some grips. I had put one on my SR25 when I had it and it worked pretty good. I cannot remember what it is called, but if I see it in Brownells, I will come back and post it up.