I got the Bolt Carrier Lock-Back Blues
Sounds like you should be drinking a beer when you hear my blues? Well, go right ahead. Have one for me also.
I just assembled a 14.5 inch AR with mid-length gas system. My gunsmith put on the gas block and the tube. The BCG is an NB-finished Fail Zero unit (full auto configuration) which works fine in another mid-length AR. The loading, firing, and ejecting goes without problem. But the empty magazines showed a problem with the BCG locking back.
I started with an H buffer and an extra strong Wolff recoil spring. The problem was that it almost never locked the BCG back on an empty mag. This happened with several flavors of Magpul, with a Troy, with a couple of different versions of Lancer magazines.
But the basic GI metal 20-round mag, with original design follower, always raised the bolt hold-open just right. It never failed to lock the bolt carrier back.
I started changing the weight of the buffer and the spring. The hold open problems continued but the Lancer mags started to do better. So now the gun has a normal weight carbine buffer and a normal strength carbine spring. The Lancer mags hold the BCG back most of the time, but not 100% of the time. The Troy and Magpul magazines still do not hold the BCG back.
And again, the basic GI metal 20-round mag, with original design follower, always raises the bolt hold-open just right. It never failes to lock the bolt carrier back.
Sometimes the failures let the BCG go all the way forward and sometimes it seems to hang up on the actual magazine follower. In other words I find the BCG just a little forward of the normal open position, and when the mag is removed the BCG slams forward. There are also scratches on the rear ramp of the highest part of the mag followers, except the GI one. The scratches look like a bolt lug is catching the follower so that this sometimes causes the BCG to stop forward motion above the empty magazine.
Any idea as to whether my BCG is moving too fast, or too slow? Think I can improve things by putting in a light-weight Seekins BCG? Should I be going back to my gunsmith and asking blunt questions about gas ports being misaligned?
Thanks for any and all thoughts on this.
Bart Noir