Get an M1 Garand and a preban AR15. Put a t37 military surplus flash hider on the Garand. It is .30-06, so it shoots farther than .308 or .223, is semiauto, and you can legally put the t37 on. It just screws on in place of the gas cylinder lock. I have 2 all GI Garands and a third one that had a match barrel on it when I got it. Since it wasn't original, it wasn't too much of a sacrilege put a B-Square mount and scope on it along with the t37. Works great. I can shoot 3-4 inch groups at 300m and I ain't that great a shot.
I prefer the AR configuration, but have never been a real fan of .308. Combine that with the fact that you can't get a preban AR10 for the flash hider and thus my recommendation for the .30-06 Garand. For an old gun, they still shoot sweet and are still less expensive than an AR10 or a preban M1A that you can put a flash hider on. Also have a .223 bolt and .30-06 bolt and am having flash hiders put on both, which is legal since they aren't semiauto. I got the 2 bolts in those calibers to match the ammo I already use.