Springfield armory used to make one, called the M-1A. Semi auto version, had the magazine etc. Was esentially for targets but looked almost like the real deal and was very expensive. Don't know if they still make it or not. Probably good google and find out fast enough.:)
I was very lucky to buy a Springfield Armory M1A .308 semi auto (civilian version of the M14) several years ago, it also came with a rare Choate folding stock and with a Leupold tactical scope.
sweet!
sweet!
sweet!
As far as stopping power with crazed fanatics its either a lot of really small supervelocity rounds or flechettes or a single high mass round.
Recently there has been lots of news of the MetalStorm system, perhaps 25-50 round bursts would be better from a multi barreled rifle? or better yet develope a battle rifle using railgun technology firing hyperspeed rounds, similar to the ones in the Swarzennegger movie, they do exist though probably still not too portable.
Either that or use caseless ammo with exploding heads.
For my bear hunting ammo in Alaska I prefer the Barnes X bullets that spread out like a high speed propeller and leaves a huge hole for maximum blood loss.But thats the .338 and .375 rounds.