My Dad left me a trapdoor 45_70 that he’d gotten from a studio sale in Hollywood in the 1940s. Also he had an Ideal handloader for it. I make my own black powder cartridges and fire it once in a while. Never use anything but black powder in a trapdoor. Even light loads of smokeless powder can build high levels of pressure. In other words never use ammunition that isnt specifically designed for the firearm. It is painful to have to say this.
I really like the Trapdoor. Is yours the carbine, or the rifle?
I have a repro rifle (Pedersoli). That thing really reaches out there with black powder rounds.