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I think you could compare it with a trapdoor springfield. The gun takes a paper cartridge which had a felt disc at the back to seal the breach. The primer flashes part way forward on the powder charge and they had to use a special primer because the then available standard ones were not hot enough to dependably burn through the paper cartridge. I have shot one of the rifles using loose powder and a base wad cut from a muzzle loading shotgun wad. In that configuration it shot well and the breach did not leak.