Make sure the barrel is clean all the way down, pull the breech plug and look. Could be when you shoot it is forming a crud ring just above the powder charge, swabing between shots helps. Also get an extension for the ramrod, it will help with the loading or when at the range get a longer range rod. If the bulet is not firmly seated on the powder and there is an air space between the bullet and powder that could cause a presure spike when it fires, resulting in a bulged barrel or worse.

Accuracy, you may need to experiment with different bullets and sabots and powders and powder charges and primers to find a good load. Some guns are easy some are finiky. And some just never will shoot good. Loose powder is a lot less expensive too and much easier to customize your loads.