WHAT DOES BCM LOWER RECEIVER MEAN?

bcn complete lowerI thought lengthy and difficult just before I bought this lower! The Spikes tactical lower's are above $100 more affordable. That's what I chose the last time. The spikes labored a hundred%, but Once i obtained it I wished the bcm. Ended up trading the spikes lower to get a pistol at my lgs. Saved my cash and got the bcm when it c