Okey dokey. The getting around the gun laws bit I understand. My muzzle loading pistol ( see the thread below) was built for similar reasons.
http://forums.nitroexpress.com/showflat....true#Post121261

Why not threaded all the way was for the reason that you mentioned. To get a really good joint I tinned both threads and assembled it all hot. Now that is not too bad on an inch of thread but a bitch potentially on the full thing. The first barrel is OK, but you need to make an expanding brass mandral to fit inside the barrel for the second one to get enough purchase to wind the hot barrel in. Secondly you don't need to. 1" x 7/8 BSF is not far off a SR mauser thread and that is good for 60K PSI without the solder. Concentricity is going to be a problem perhaps with a full thread because of the tapers involved. To single point thread it would need too much jigging and messing around. I just shortened the mandral (tenon) and run the tap in with the tailstock.
Watch the wood on the Zabala at the head, it is not the greatest design for heavy recoil.

Good luck with the project.