This is largely a means of grinding from the reinforcement content that was extra to improve the buffer tube/extension place, and reprofiling the area to really make it resemble the initial A1 place. This could include some welding or filling of some form. Use the pictures under as an example: https://immensedirectory.com/listings516889/the-smart-trick-of-colt-combat-elite-commander-45-acp-that-nobody-is-discussing