BigBill, R&D and Kirst both make cylinders to covert most Cap & Ball revolvers to cartridge. The 44 C&B bore is actually 45 caliber, and the 44's convert to 45 Colt. The Navy converts to 38 Long Colt or 38 Special, but must use a hollow base bullet as the 36 bore is 375 and the 38 is 357. To shoot 44 Special or Russian, the barrel would have to be relined, and could no longer function as a Cap & Ball unless you made new cylinders. No Cap & Ball design is strong enough to handle the 44 Magnum except maybe the Ruger Old Army.