The original breech block is rimfire and shot the same round as the Sharps & Hankins - No. 56 Spencer. Since I still wanted to shoot this and use it for reenactments, I got a centerfire block from S&S. The blanks used for reenactments are resized and modified 32 gauge shotgun shells with 40 grains black powder. The live rounds are cut-down 50-70 Government cases with cast lead bullets.