We've done a few. I've actually taken the time to model the barrel extension and run it through the 3D printer. If we had more demand for the work I'd put em into production. I guess its a chicken/egg thing. I had a small gaggle of barrel blanks made up that I've sat on for almost a year now. I literally just sent them back for contouring last week. Turning them into RV's instead.
If there's demand, I'll run a batch, but it's not worth investing any real time/money into for one or two.