Shimming it takes no time at all and even though it should come ready to go, i wouldnt be shipping it back myself. If i was going to be sending anything off it would be that breech plug to someone to install a removeable ventliner or the whole gun to bestill customs to have him fit a bushing plug to it. If you are worried about accuracy and you are shooting bh209, i would be getting something better than the factory plug with the brazen vent.