I'm new to the Forum, but I think this is the place I need to be to get the answers I need, to reload for the Springfield Trapdoor I just bought from my next door neighbor. I think it has been reworked by someone in the past as its dimensions are different from any I’ve seen in my reference books. There are no markings on the breach, no cartouche marks on the stock. It has two barrel bands. The forward one clamps in place. It has sling swivels. There is 14 1/2” between barrel bands. Trigger pull 13”, stock length 39” barrel length from breach 26 1//2”, total length 47”, muzzle diameter .799, lock plate marked 1863 with a faint eagle visible, US model 1864/1864 rear sight, the muzzle is 1 ¾” past the fore end cap. I removed the barrel from the stock and discovered B1 on the barrel and breach. All metal is a deep black and the bore looks new, with three groove rifling that slugged .512. Now my questions: Any ideas as to what I have? Is the rifle possibly assembled from loose parts. It looks to me to resemble a Model 1866 Short Rifle but measurements do not match. Any books you’d recommend on reloading the beast. To reload for it, should I go with a .512 or .515 bullet? Is it advisable to get a .512 sizing die and open it with a brake cylinder hone for a .515? What reloading die set has an expander plug for .515 bullets. Seems to me I read some where a company makes a .50-90 set that expands to .515, but I can not find the information now. I am also looking for a good source of 1-30 and 1-40 lead. Any comments on bullet moulds the 450 and 500 gr. ones would be most helpful. I'd like a good Military style bullet and one with a large flat point around 500gr. for hunting.