Mostly good but not perfect. - Bushmaster .450 Bushmaster Upper Assembly w/5-Round Magazine

Upon receiving my upper I see it has a low profile gas block instead of one with rails like whats pictured. I field stripped it to clean and inspect and what I noticed was that the coating on the bcg was a little rough but nothing too crazy. Put a light coat of clp on everything and call it good. Loaded up the provided mag and could only get 4 rounds in. Thinking that’s odd considering it is supposed to hold 5, I gut the magazine and what do I find? A 5.56 follower on the bottom of the mag spring! Sweet! Gotta love freebies! Ok, so I make it out to shoot and I load 3 rounds in the mag. Put the mag in the gun, pull back on the charging handle, let go... and failure to feed. This continued to be an issue for the first few mags while using the charging handle. If I locked the bolt back before inserting the mag and used the bolt release there weren’t any issues and eventually things broke in enough that using the charging handle was fine. Another thing to note is that other reviews have mentioned sharp feed lips on the magazine. It doesn’t feel excessively sharp to me, but I was finding slivers of brass every time I cleaned the bore so they might be on to something. Lastly, it seemed pretty accurate but by the time I got the scope somewhat dialed at 100y, I was getting a little recoil shy. 60 rounds of 30-06 in a session starts to become uncomfortable, 40 of .450 made me not want to shoot it anymore. I see a muzzle brake in my future.