WHAT DOES BCM LOWER MEAN?

bcn complete lowerI thought extended and tough ahead of I purchased this lower! The Spikes tactical lower's are above $one hundred more cost-effective. That's what I chose the final time. The spikes worked 100%, but when I got it I needed the bcm. Ended up investing the spikes lower for a pistol at my lgs. Saved my cash and received the bcm when it