Greg. I asked them about their thinwalls and use of steel and the answer was no. Only way to do it and be safe was to have the barrels threaded and the choke portion extended past the end of the muzzels. JW
I asked specifically about this when I had mine installed since it was on an older target gun. I don't really care what my hunting ammo costs since I use comparatively little of it, but if nontox were required for targets it would put me out of business so I wanted my gun to have the ability to shoot steel or other hard shot. They told me that their regular thinwall tubes were not steel-compatible, but that I could purchase steel-safe tubes to fit the existing thinwall threaded barrels at any time, and those would be safe. If this is a concern you can simply buy the steel-safe tubes when you have your barrels threaded. I don't know if the steel-sdafe tubes are necessarily extended, I had thought they could be purchased flush, but am not sure--a trip to their site should confirm that.