The upper can be a flat leading, obviously, and includes every one of the conventional Mil-Spec exciting stuff just like a dust go over and forward aid. It truly is a standard FSB and no I had no issues sighting it in. I at first crafted it with a DPMS https://archerkcuem.blogoscience.com/32693759/5-simple-statements-about-colt-10-5-inch-9mm-smg-upper-receiver-assembly-explained