I originally had a BM AK brake pinned on my PostBan 20" Colt. But when BM came out with their new Mini Y-Comp, I wanted that instead. I much prefer the looks of the Mini Y-Comp, so I took off the old brake and sent the upper off to BM to have one installed.
They refilled the pin grove on the muzzle end before pinning on the new brake. The cost was for the new brake and return shipping.