I built my own smokeless muzzle loader a few years back (actually built a barrel for a H&R), and one of the things I found critical to accuracy is primer type and breech plug design. I found that large rifle primers are much cleaner than 209's (of coarse) and are far more accurate, in my rifle. Not many people understand the pellet theory, most think that they are for covenience of loading, which they are, but they also allow for a faster burn if the gun is set up for as in the Ultimate. They can only get there speed from pellets and not from powder, powder is a progressive burn for length tolerant barrels, the longer the barrel the more powder it will burn, pellets ,on the other hand, stacked on top of each other with the hole in the middle start burning alltogether at ignition, causing what Busta says, detonation, or in other words everthing blowing up at once. I didn't copy the ultimates breech plug design, but I do use large rifle primers.