This is a very small case, so small that most people would never believe it has a rifle inside, which is a very good thing when you are trying to keep a low profile. But it’s also a very snug fit. My lower has an aftermarket grip that is slightly longer than the standard A2 grip. As a result I had to crush some of the protective lining and wedge it in the case to make the lower fit. I tried an upper with an aftermarket muzzle brake and it would not fit, but one with a birdcage flash hider fit well. For a standard M-4 style gun with a 16-inch barrel fitted with a flash hider and a collapsible stock, this is the best option. However, if you deviate much from that, you may need one of their larger cases.