Any of you that have the BCM 20" A4 upper assembly…
What kind of accuracy are you achieving with it? At what distances?
Ammo that your using?
Thank you, TGR
I had one for about 10 days before I (sadly) sold it for cash for another build. I was getting about 2.5 MOA from WWB .223. With my friend hand loaded 75 grain stuff, I was easily getting sub MOA off a bench with a TR21. I had a Larue handguard on there FWIW.
https://www.m4carbine.net/showthread.php?t=82746
My 20" was shooting 6" groups at 300 yards with M855 and a 4x ACOG.
At the time, I considered that bad. 
FWIW, my 14.5" shot better though.
I must be spoiled… I feel like a 20" needs to be 1-3 MOA at 200-300 yds. Gotta love what ol’ retro Colts can do to you… at least in my case.
I’m considering doing a BCM 20" but I may have to go stainless BCM.
MOA doesn’t really change over distance. 2-3 MOA @ 10yd = 2-3 MOA @ 1000yd. Group size and distance are proportional.
I get 7-8" groups at 100yd, but that’s with a non free-float (KAC M5 RAS), a TA31RCOA4, and I’m a bad shot as it is. :blink::haha: :sarcastic:
Upper receiver group is this: http://www.bravocompanyusa.com/BCM-M16-Government-20-Upper-Receiver-Group-p/bcm-urg-gov-20.htm
Basically true. But sometimes the rifle will barely stabilize a bullet which will be fine at short ranges, but increasing instability will open up MOA at longer ranges
This happens at shorter and shorter ranges as the barrel gets worn out. I would put a worn out barrel groups opening at 200 yards, and that is after 20k rounds or so.
I’ve found good accuracy with mine. I have an NM front post, and it does about 1" at 50 yards, if I’m having a good day.
I appreciate the replies regarding the uppers performance.
I have pretty much a complete bcm 20 inch gun(just has a armalite a2 stock as bcm was only selling their lowers with m4 stocks at the time). Mine is wearing a kac rail and has an a2 carry handle on it.
Generally under 4 moa with random 55gr ammo at 100 yards if the shooter does his or her part. I haven’t shot match ammo through it to group so I can’t say what it is capable of. As of late I’ve been shooting stuff like silver bear through it to get rid of it as I don’t trust it in my 10.5 suppressed ar. With that in mind accuracy isn’t that great but the ammo is to blame.
about 3 moa withvlaue type ammo, and about 1.5 moa with some 68 gr match ammo.
I’m honestly not the world’s best shot though. I think someone else could honestly get a better group with this rifle.
MOA doesn’t change, but a rifles accuracy can as distance increases.
I feel like a 20" needs to be 1-3 MOA at 200-300 yds.
me too!
6 inches at 300 yds is basically 2MOA. 
I plan on doing a 20" A6 someday. I know you asked about the a4, but I am in love with the a5 setup.
I have not got a chance to go past 100M with it yet, so I guess I have no real indication of how it will preform. I suspect it will hit min of man out to 800M if I do my part.
Milspec accuracy for the M16\M4 rifles is 3" at 100 meters. Most rifles shoot much better, but that’s the floor. Some of the worst ammo for accuracy is issue M855. The non concentric placement of the penetrator gives this load a wandering windage outside of 100 meters. Regardless of how good your barrel is, or how much magnification you’re using, you start to get football shaped groupings that only get wider as the distance increases.
In 15 years of shooting USGI issued rifles and ammo, I’ve run across two or three combinations of rifle and ammo that produced reliable MOA groupings. It’s really fun when the pits radio back that they’re repairing your target because you keep shooting the spotting disc, but it happens so rarely that you can’t even begin to rely on it.
This is the kind of setup that I’m thinking of…
I’ve got the glass and rings and a complete spare lower so I thought about putting together a “Poor mans” DMR.
I know of all the other more qualified choices regarding precision uppers.
Cost is the main factor…
A reasonably price upper assembly made of quality components that will get the job done.
This doesn’t make sense. How does the accuracy of the rifle change without the MOA changing?
loss of velocity plus wind and drag I would assume.
Going subsonic at long range can. Although it’s not really the rifle’s mechanical accuracy at fault (unless it was marginally stabilized in cold dense air). The external conditions can affect groups like wind, ect.
For my post I was merely applying the high school teachers’ ideal situation of a frictionless vacuum. The real world does indeed wreak havoc with perfection.