"The Real Deal"
Yeah heavy buffer, my bcg also has weight installed in the rear of it secured by a roll pin.The buffer I used was the standard 9mm buffer that Midway carries. It needs to be heavier than a standard AR carbine buffer. However, I used a standard carbine buffer spring.
Recoil was very tame and the brass was tossed very clear to about 4:00.
Good luck with your build.
I woukd also recommend a bolt carrier that is ramped on the bottom, which allows the use of just about every trigger on the market. The original colt design requires a 9mm specific hammer or 9mm specific fire control group, will not work with many others. Mine is the old style, but one day want to upgrade to the ramped version, rock river arms sells both.