The Remington 7400, and its semi-auto predecessors, are notorious for jamming after every 25 rounds or so, unless you clean the chamber very thoroughly, with the chamber brush provided in the box.
Deer hunters who only fire one box a year to sight in, and then clean the chamber, are happy with these rifles because odds are that they will never fire more than 5 rounds while they are hunting. But, as a tactical weapon, this rifle would be suicide. Moreover, the mechanical design is based on one piece of metal "peening" (hammering) against another, until the rifle action beats itself to death. I have heard that about 1,000 rounds or less is not uncommon.
As mentioned in a prior post, the Remington pump 7600 (and its predecessors) are as well built and reliable as the Rem 870 shotgun. In other words, they are as solid as tanks. Get one with a synthetic stock if you are going to be throwing it around. Either .223 or .308 would be fine, though the .308 may kick somewhat in this rifle.
Best Regards,
Mannyrock.