I went to the range today to try out my primary M-4gery build and just wanted to post my thoughts about the gun now that I have it almost completed. Here’s the spec’s on what I have…
BCM M4 A3 upper w/ ”F” marked FSB
Daniel Defense auto BCG (thanks Grant)
LMT rear sight
TROY MRF DI rail system with Magpul ladders
VLTOR offset mount with Surefire G2
Eotech 512
Bushmaster carbine lower with carbine buffer.
The upper and BCG are practically brand new so my goal really was to determine reliability and assess function, with a secondary goal of looking at accuracy. On this outing I took Wolf black box 55 grain FMJ. It seems to be the worst offender for a lot of folks since it is underpowered and dirty, so that was the reasoning for my choice. I wanted the worst-case scenario in ammo so I could determine a baseline for the carbine.
This isn’t a real high round count test but all told, I fired 220 rounds of the Wolf black box with absolutely zero (as in none) failures of any type. Even the first round from a brand new BCG and almost brand new upper gave absolutely no problems at all. Each subsequent round fed and fired without coaxing or cursing. Each empty ejected good, landing at my 4:00 position and about six feet away. I am absolutely impressed with the function of the unit, even without a real break in period. It did what it was supposed to do. It just ran.
Accuracy was better than I expected considering the ammo. I wasn’t going for pinpoint accuracy but from as far out as 200 yards benched & slow fire my groups were pie plate sized with irons and a little better with the Eotech. Not bad with what I consider economy practice ammo. The Troy rail and Eotech were rock solid with zero movement and the Eotech co-witnesses with the irons. The LMT sight is also rock solid and was almost right on target straight out of the package. Not much to do but mount ‘er up and tighten it down. A pin drop of thread locker keeps it from backing off.
Breaking everything down after the session I found very minimal and even finish wear along the BCG rails and very minimal finish wear on the receiver races. Nothing appears out of the ordinary and all parts apparently mated very well, as evidenced in the field strip. The parts were sooty but there was nothing “caked” that didn’t easily come off with Breakfree. The chamber cleaned up with no residual carbon with little effort, no more so than with good, clean ammo. There was no other visible wear on the BCG or the receiver. There is no wear evident on the extractor with the finish still intact at the claw.
Overall I am extremely happy with the M4 setup. My last task will be to swap out the lower for a BCM lower but I’m in no hurry at this time. Hope this helps someone that might be considering a similar build or similar parts. I’ve got many more rounds to run but I’m fully confident this setup will continue to make me smile for a long time. Thanks ! 
