You can use you M1A/M14 in any division you like. Most have 223/556 as a minimum.
USPSA has Multigun Heavy Limited, which is an iron sighted 308 ( or larger) with a 20 round max mag capacity, 12 gauge pump with an 8+1 max capacity, and a 45 pistol limited to 10+1.
They also have a Heavy Optics class which allows optics on the rifle, a .40 cal pistol, and semi auto 12 gauge.
I shoot Heavy Metal and there are usually no more than half a dozen shooters in my division. It's expensive, but very satifiying to be able to hold you own shooting against the guys shooting the hot rod 223's, high cap 9mm's amd semiauto shotguns.