I decided to go to the local range and try out the new Bushmaster upper. It's been raining here for several days and is scheduled to continue for several more. Because of the weather I limited my shooting to seeing how well the new upper shot, it's reliability and to look for potential problems.
First, the Bushmaster upper fit on my M&P-15 lower like it was made for it, snug, with no excess play but not so tight that I had to force it into place. I shot various plate size (11") targets at ranges from 50 feet to 50 yards using the two factory supplied 26 rd magazines. I fired a total of 100 rounds using several brands of ammo, mainly Wolf & Tula. Aside from an occasional flyer, all hits were within a 2" diameter circle of the point of aim and there were no feed or ejection problems. I did not fire any long runs since this is a new and untried upper, though I did fire a handful of 2-3 round quick bursts. About half the shots were fired as slow, aimed fire. The remaining shots were either the already mentioned quick bursts or 3-4 round aimed bursts. Recoil was definitely more noticeable than firing a 5.56 and there is also a noticeable difference in noise level.
This gun was not a tack driver. OTOH, I wasn't going for accuracy today either. Besides, I was using the factory iron sights and $6 a box Russian ammo, not exactly a combo noted for precision shooting. FWIW, in the Bushy upper I am not looking for a gun that shoots sub 1" groups at 500 yards. Instead, what I'm interested in is "combat accuracy". For me that means consistently hitting a fist size target at 100 yds or less. Reliability was excellent, though after only 100 rounds the reliability question is still not fully settled yet. Fit and finish seem excellent. To look at it when it's installed on my M&P lower, you'd think the BM upper was OEM from S&W. As I mentioned earlier, I just ordered two more magazines from the Bushmaster web site (they were actually in stock!) to go with the two I got with the gun.
Overall impression... I like it. At this point, it looks like this is a keeper.