While I have never felt "confident" of buckshot on deer, any load for modern 12 gauge guns can be duplicated in a muzzleloader. Try 80 to 100 grains of 2f black or "RS" pyrodex powder, but not exceeding the recommended maximum for your gun. Seat two hard card overpowder wads and a fiber wad if you wish but the fiber is not necessary and often will spoil the pattern. Then drop 9-12 pellets of 00 buck or the appropriate number of any other size buck. Top it all off with an overshot card or one of your overpowder cards split to half thickness, they split very easily. Then shoot on a large cardboard target at least three feet square so you can see all pellet holes. Because every gun is an individual it is not possible for anyone to tell you exactly what will shoot "best" in your individual gun, only actual loading and shooting and keeping records of the results will tell you that. Some folks like the plastic shotcups and claim they improve the pattern. I've never found that to be true in any of the several dozen ML barrels I've tested but if you do choose to go that route do be sure to load at least one overpowder card under the plastic wad. That will provide a better gas seal and reduce the tendency of the plastic to melt from the more sustained heat of blackpowder making clean up much easier. You can't buy success, you have to do a lot of shooting to work up the "best" load, however, you may also find the very first load you try will be "good enough".
You don't mention if your gun is choked. With a modified or full choke you should have no trouble getting effective 30 yard patterns but if it is a straight cylinder bore it's likely your pattern will sperad too thin to reliably reach 30 yards. Again, only actual testing will tell. It's been my experience that smoothbores are even more quirky individuals than are rifle guns.
