Well it doesn't have a rad to match the tap on the end so either it sits in a counterbore and there is a small plain bore before the pellet reaches the barrel which would need opening upto .25. or you screw the barrel in till it butt's up against the tap to form a seal but then you probably couldn't open the tap for interference from the barrel. You would clearly see the end of the barrel with the tap removed if this was the case.