Always use a clamp on crosman breechs, you will have to remove the trigger assembly so you can get the clamp just behind the loading port to put the pressure as close to the breech as you canJust remember when you go to pull it apart at some point that you need to reclamp it in order to loosen the breech screw
The transfer port (ring) may be a loose fit also... When I upgraded my Phase II to a steel breech, I had to replace the barrel and the transfer port to a newer style so that everything would match up...
Looks like I'm going to have to convert this to 22 if I really want a selection of barrel lengths without out going custom. Found one reference to a 14.5" .177 barrel that came on the Crosman 1389 Backpacker. However the parts diagram doesn't really show the lead-in on the barrel. The breech on this gun was completely different doesn't appear to use a bolt at all. Anyone had one of these and taken it apart?
You use a clamp because you cant properly tighten the small breech screw tight enough to seal up the transfer port. So you use the clamp to clamp the breech to the airtube and then tighten the breech screw. When you remove the clamp after tightening down the breech screw. The breech and airtube will naturally try and push apart from each other but they cant because the breech screw is screwed in and holding them together and its screwed in further then if you didn't use a clamp, also the force of the breech and airtube trying to push apart locks the breech screw in place so it won't loosen up over time.A lot of out of the box disco's had bad groupings and the cause was a loose breech screw right out of the box
The 1389 barrel will fit perfectly but it's been out of production for a long time.... There is no 14" barrel available from Crosman in .177 cal AFAIK.... You can get 10", 18", and 24".... It's simple to shorten an 18" and recrown it.... Bob