I have a .62 caliber smoothbore (20 gauge) which is a Green Mountain Barrel that drops into my T/C Renegade stock. A nice shooting shotgun and it throws a mean round ball also.

You might want to keep your eyes on the auction sites. Sometimes a CVA Trapper or Gobbler will come through there reasonable. Sometimes not so reasonable.

Thompson Center does make a few sidelock shotguns but they do tend to cost a lot more. That is why I went with the Green Mountian drop in barrel.

good luck in your search I will be grouse hunting this year with mine...