My best friend is at MARSOC, they use M4's, with 77gr SMKs. 14.5" barrels Heavy M4 profile, free floated, and Surefire suppressors "they are nice guns". They have had SCARS drop mags out of there guns when they get hot I guess cause the lower. I really like the 77gr match kings War Legal to. Get rid of the green tip crap with the steel tip.
I like the Green Tip myself...
Kinda like a Hot Knife and butter on Armor...