My vote goes to an AR-10. But there are other rifles that may fill the niche. I am assuming you're thinking of a gas gun. The M1A is also a solid choice. It can be justified that in the event of WROL, a battle rifle with superior capabilities to a 5.56 may be needed. The way I see it, even the Marines have M4s and M1A EBRs in one squad. I own a gas and bolt gun in .308. It just made sense to me, though. I think given enough thought, we can rationalize just about anything
