Wetibbe,
Perhaps you're not familiar with the Thompson Encore. It was designed with interchangeable barrels. It can be converted from Muzzle Loader to Center Fire simply by changing barrels. In fact it also accomodates a shotgun barrel, or conversion to pistol barrels as well. The barrels can be had for a fairly reasonable amount and would be potentially an excellent choice for determining his ability to handle the recoil of the round. The barrels hold resale value quite well and if he determines he can't handle the recoil or just wants to get rid of the barrel he can sell it quite easily. As a result, I think it's an excellent choice for his purposes.
