The British cartridge for the P-53 musket was much prized by both sides. In the early 1850s, the laboratory at the Royal Arsenal at Woolwich solved the fouling problem. With correctly-constructed Enfield cartridges, fouling is controlled and the generously-undersized Pritchett bullets are easy to load, regardless of how long you've been shooting. It is night and day difference when compared to shooting American-style Minies. The only time I revert to Burton style Minies is because of the rules against paper cartridges on some ranges and in NSSA and NMLRA sanctioned competition.
Brett Gibbons' books are most recommended.
The Destroying Angel: The Rifle-Musket as the First Modern Infantry Weapon
The English Cartridge Pattern 1853 Rifle-Musket Ammunition