my red- x 308 barrel. I am having feed problems. I have fired two single shots so at least I know it goes bang. I ordered a couple of different manuf. mags, nothing to do with the barrel. Ihave a Leopold 6x18 scope. Let me know how that scope does on the ar-15, as I have the nikkon p-600 going on a 20" colt upper(ae-15), another build.