Colerain makes a nice turkey choked barrel. I have never used one, but seriously thinking about it. The following is copied directly from their website;
For many years now we have been producing turkey choke gun barrels. These barrels are for shot only due the tight restriction at the muzzle. We offer these in 20 gauge bore that restricts to 58 caliber at the muzzle. We have had nothing but wonderful success with these barrels. For those of you that love turkey hunting and muzzleloading then you should try this. Will you be handicapped? Only in the fact that you will be limited to one shoot unless you build yourself or have someone build for you a double barrel. We know builders that can do this. From all the feedback we have received from builders and hunters that one shoot is the only handicap you will have. These barrels are capable of, and do with the right load, out shooting modern turkey guns. The shoot patterns are extremely tight. The gun builder that started us down the road on these choked barrels said from the beginning that the firearm should have both a front and rear sight, not just a front bead. I know many might ask if 20ga is large enough. Yes, once again, we are dealing with a muzzleloader that we can shoot various weights of shoot through. You can even try taking it to your local turkey shoot. They might laugh at you going in, but if you can make them feel pity for you and allow you to shoot, they will ask you to not bring it back. This story did happen!!
The following loads are a sample of some being used in the field by customers.
Shown below in the order of steps taken.
100grs FFG powder
3 to 4 .125 card wads
2oz #6 lead shot
½ or 1 .125 card wad
80grs FFG powder
2.125 card wads
Styrofoam wad**
1 3/8 #5 lead shot
1 over shot wad
80grs FFG powder
1.125 card wads
1 felt wad
1oz #4 lead shot
1 over shot wad
Notes:
The .125 thick card wads should be moist. Most hunters will just suck on them till moist. They should then be started through the muzzle and the choke on there edge with a short starter. Do this one at a time if using multiple wads. Once past choke, ram all at one time onto the powder. Wads need to be seated TIGHT on the powder.
One load shows ½ to 1 .125 thick card wad over shot. The other 2 use an over the shot wad which is thin. Either will work, just make sure that everything is packed tight. You do not want your shot running out onto the ground as you walk. That might make the turkey happy, but I doubt you will be!!
** Styrofoam wad
This is made from the Styrofoam board used for insulation. ¾ to 1 inch thick. Using whatever you can find to punch out 5/8 dia. plugs. This serves two purposes. First, helps cushion the shot, preventing deformation, second, reduces felt recoil greatly