Follow up on this thread: I contacted Briley tech service and they sent me a CAD drawing of the One Shot with measurements. It was a 1:1 sketch so I printed it, cut it out and using it as a template it looked like it would fit. Ordered the One Shot extension and it came in last week. it FITS! For clearance I have to install the One Shot extension first then screw in the Carlson choke. Just enough clearance doing it this way. Now that it it fits I had to address the issue of not getting the last round in the magazine. Thanks to the info from @Birdog19 post in this thread I was able to shorten the magazine spring without a lot of trial and error. Shortened the spring to 16" sticking out of the magazine and it fit 8 rounds but it felt like the last round was binding the spring just a bit. Cut the spring back to 15" and it leaves some clearance after the last round. Good to Go! I'll hit the range tomorrow and runs dome rounds through it. Pretty happy with the outcome though.