First off I would ignore any references to modern shotguns, and modern trap shooting, none of it pertains to what you seem to be interested in. The plain facts are that small gauge shotguns make a longer shot string. This is a problem when wing shooting, but not so much with more fixed targets like turkey, and squirrels. Smaller smoothbores produce a tighter pattern, without going to the non authentic period incorrect jug choking camp. The advantage of a muzzleloader is you have total control of what a given charge will be, unlike modern firearms, so you have a lot of variables to tinker with.
Instead of building a plain grade trade gun, that as has been mentioned, will be troublesome due to the lock verses barrel size issues, think about a slender more elegant chiefs grade. That would allow you to use a more suitable small English, or French, lock depending on which style you prefer.
Hungry Horse
