It doesn't matter if you get a glock lower or a colt lower both are great, the most important part is the BCG and make sure its milled properly. I had had a lot of issues with the weights in my buffer ,then destroying buffers. Solved by quarters and a heavy buffer. My 9 shoots like a machine gun !!!!!! No BS ! I can't feed the beast fast enough ! Currently I have zero rounds of 9mm not loaded into handgun mags.