Howdy, Pards,
This may NOT be much help as Lyman no longer makes the mould I use (533476AX), but the principle might help if you can locate the right mould or have one made. When I discovered that M1860 carbines have a tapered bore, going from about .545" just ahead of the chamber to .535" at the muzzle (22" barrel), and I did NOT want to use heel bullets, I discovered that using hollow based bullets with a cast diameter of about .538" and the inside of the case necks reamed for about .004" smaller than the bullets (I used cut down .50-70 cases, which make the walls thicker at the resultant new mouth of the .56-56 cases), would allow the rounds to chamber (I sometimes had to run the finished round partly into the sizing die), and produced quite acceptable accuracy, even using smokeless powder! With BP and a .535" bullet the hollow base slugs should expand into the grooves.
BTW, FWIW, and while I do NOT necessarily recommend the use of smokeless powder in these original guns, I have found that the internal volume of cut down .50-70 brass (Dixie Gun Works older stuff), and the Relative Sectional Density (weight in grains, divided by 7000, divided by the square of the diameter of the bullet) of most of the suitable bullets are very close to those of the .45 LC! A commonly quoted charge of Unique produced velocities in the 850 ft/sec range for the 411 gr. bullet. BTW, I cast these out of #2 alloy, rather than softer, as I seem to get better results! IMR 4227 also produced good results with this bullet design.
Regardless of what loads you use, you must crimp the case mouth firmly, and prolonging case life of cut down .50-70 brass requires annealing the upper half of the case. I set UNprimed brass on top of a pill bottle, filled with water so it won't float, set in a pot of water so that the lower half of the case is submerged. The pot is on a lazy susan, so I can turn it by hand. I use a propane torch aimed at the case mouth and what is above water level. I turn the lazy susan and when the case discolors (it probably will NOT turn "cherry red"), knock the case off the pill bottle into the water to quench in the anneal.
As long as you don't try to magnumize the loads, you can get pretty good results using CAS-level data for .45 LC for the .56-56 and .56-50. [I can assume no responsibility for the use of the above information in guns other than my own, and maybe not then!
Hope this helps.