Well, did you take a choke out of the barrel before trying to install your new choke??? You mentioned that your starting to wonder if the barrel uses screw in chokes, so, if you didnt take a choke out before trying, chances are it doesnt. Does it say "Full""Modified"or"improved cylinder" anywhere on the barrel? Hopefully yu havent shot the gun with no choke in the barrel, if you have and it needs screw in choke, you have probably ruined the threads. Hopefully this helps you some.