Hey all. I am having a strange problem with a 20" BCM upper and BCM bolt carrier group. I put this rifle together last spring and have put around 700 rounds through it. Today I go out and after 15 shots, it begins to short stroke. I figure it is dirty or dry (even though there are only 15 rounds since cleaning and oiling) so I pull the bolt, wipe it down and re-oil with LSA. I have used LSA on all 5 of my AR's and it seems to be good stuff. Anyway, still short stroking and finally no-stroking. The damn thing is a bolt gun.
I'm not one to be discouraged so quickly so I pull the BCG from one of the others (it is the same but M16 surplus) and the gun functions flawlessly for a mag dump.
Thinking it is the BCM BCG, I stick it in the gun I took the other one from and that one works flawlessly for a mag dump. I put the BCM one back in the BCM 20" inch upper and the same thing, no stroke or extremely short stroking. It so short that the shell doesn't eject but I can here a slight spring rattle in the stock so I know it has moved somewhat.
I come home, take off the flash hider, punch out the pins on the front sight/gb and pull the gas tube. I even take the gas tube out of the front sight and it is not plugged in the least and lines up correctly. I checked the gas hole in the barrel and it is obstruction free. I put it back together, take it out and the same thing.....short stroke or no stroke.
For shits and giggles, I have brought a third rifle with me and swap the carriers. Again, both rifles function flawlessly with the BCG's swapped. I am at a total loss.
The stock on the offensive rifle is an A2 and it has the proper buffer and spring. I can only surmise that a perfect storm of tolerance conflicts has overcome this upper, barrel and BCG but am at a loss to explain it after so long a period of flawless operation.
I have just left the BCM carrier in one of the rifles that liked it and swapped it's carrier into the BCM upper group.
Any insight would be appreciated........