I built my barrel out of a Adams&Bennett replacement 45-70 barrel, it is 4140 chromoly steel, 1 in 22" twist rate, 26" long. I built a lug and welded it on to fit an H&R receiver. Breech plug is 5/8 fine thread with a nose on it simular to the one used in savage rifle. The SMI barrels that I have read about are all shooters. Check out "doug's message board" and look in the savage smokeless muzzleloader section for more info on the SMI barrels.