A loaded N-SSA round is basically a plastic tube that uses a minie as a stopper. The premeasured powder charge is put into the tube. The tube is closed with a minie partially inserted nose first, then the exposed skirt is dip lubed and there you are. Authentically it was done with paper and string.
To fire an N-SSA round, pull the minie, pour the powder into the muzzle, insert and ram the minie, cap, aim fire, repeat very very quickly cuz the clock's running and fastest time wins and every other unit on the line is doing the same thing. The N-SSA Musket Nationals is as close as you're going to get to a battle line engaging in live fire these days. The main firing line at our home range Fort Shenandoah will accommodate 73 teams consisting of 8 men each. Each position has a target array of 32 clays on a backer. Fastest time wins, unbroken clays count against your score. Sometimes the weather can really bring home the concept of the "fog of war" when the smoke doesn't clear out and you can't see sights or targets clearly. The following pic is from our 2016 Fall Nationals. Time was 8:30a.