Rusty- not sure what you are looking for- IIRC, it is a screw in barrel, but not intended to be easily removed. If you do not have the blocks to support the reciever, you will usually damage the reciever while trying to get the barrel off.
Don't ask me how I know that, and I won't say what you were doing behind Sheetz the other night.
Seriously- Call Dale Blankenship down on Judes Ferry Road. He does good work, price was very reasonable on swapping barrels for me on a 20 g pump last year.