Used to see these advertised many years ago......often wondered how the zero might have changed between dismounting & replacing the barrel. Does it lock up so well that it holds poa/poi, or would it have suited barrel mounted sights better instead of on the receiver? I know many were 'scoped so was that with special mounts to account for removal/ replacement without the need to sight it in again. Sorry to ask but never tried one or knew of anyone who had one to ask.