I have two 54 caliber smokepoles. The only sabot that work in my T/C Thunderhawk are Barnes ML's. The bullet is a true 50 caliber bullet making the sabot a thinner walled. Thicker sabots using 45 caliber bullets keyhole in my 1:38 twist rifle. The best accuracy comes from using 120 grains of Tripple Seven and 295 grain Aero Tip Power belt bullets.
Since your gun has a slightly faster rate of twist than mine you should be able to shoot heavier bullets with greater accuracy. When I try shooting the 340 grain Power Belts my group size opens up to about 2 inches at 50 yards. Otherwise the 290 grainer will hold 1 inch at 50 yards every time.
Good luck.
