I have shot and chonographed the Burnside carbine, the weapon carried by my great-grandfather during the Atlanta campaign (not his original carbine - don't I wish!)
I purchased cases, cast bullets, and a mold from Dixie Gun Works. The original cartridge had 45 grains of black powder tamped down in place under a card. Tallow filled the space under the 380 grain 54 caliber bullet. I duplicated this load using a dime sized card cut out of notebook cardboard, Instead of tallow, I used Crisco, and hand seated the bullets, which then chonographed 980 fps, duplicating the original cartridge's velocity. The gas seal was quite good, a problem with many breach loaders of the period.
The Burnside is a sturdy carbine, and one in good condition is not too difficult to find. Before shooting, check the nipple in the breach to make sure that the threads are tight and not rusted. Last month, at the Baltimore Antique Gun Show Burnside carbines were plentiful and priced in the $1800 to $4500 range, depending on condition.