My ideal SHTF rifle would be a 10.5 in barreled gas piston AR-15 from Addax Tactical. As far as the optics Id put something like an Aimpoint on it. The batteries for those things last forever. I like EOTechs better, but they dont have as much battery life. They both do also run on AAs though, which are easy to find anywhere. And .223 is a very popular caliber.