Hi
FWIW I have an in-line 20 gauge with a Colonial TSTK2 .575 choke. I use 1.5 oz. Federal Heavyweight #7 in a BPI shot cup with a 3/16" 28 gauge styrofoam wad on the shot/in the cup, a 1/4" styrofoam wad over the shot/cup, 75 grains (by weight and I repeat 'by weight') of Blackhorn 209 (that is highly compressed) and a Federal 209A primer to send it on its way. Pellet count was 157 in a 9.75" circle at 30 yards with the cup having 4 slits half-way down. Last year's gobbler was shot at 40 yards with no slits in the cup and was the most instant-dead motionless gobbler I've ever seen. No pellets in breast meat and head was a bloody mess. This year I'm going to use 2 over-column styrofoam wads instead of 1, it's a conscience thing.
Sorry I can't divulge make/model as is a prototype. It's properly stocked and equipped with fibre-optic sights, it's a dream to carry and sports a precision 2.5 LB factory trigger. The only drawback is that firing is a memorable event. The load used works great in my modern shotgun but not recommended for any other weapon. Last year's load was in the barrel for 9 days prior to firing.