Something I just propossed to BM1. What do you guys think?

Crazy idea for you, have you ever shot skeet with an over/under 12ga using sub-gauge tubes? Would it be possible to create a 357 Sig barrel that is threaded at the muzzle end so that you just drop it in the 10mm barrel and then screw on a cap on the muzzle end to secure it in place? Basically a sleeved barrel + the step down for the botttlenecked cartridge.

If the thicknesses allowed it this seems a simpler axnswer to producing a whole barrel.

Thoughts?