This is basically a technique of grinding off the reinforcement material which was added to strengthen the buffer tube/extension area, and reprofiling the area to make it resemble the first A1 region. This may incorporate some welding or filling of some kind. Use the images underneath for example: I say https://jeffreytwvuv.oneworldwiki.com/6357225/colt_python_6_for_sale_for_dummies