I agree that straight-sided cases are not the best for use with black powder, although it can be done. The .44 Magnum chambers are generally cut tighter than most .45 LC, but the brass will be stiffer as it is designed for heavier smokeless loads. As far as the rifle, if you, indeed want the capability for both CAS and hunting, I would recommend the .44 Magnum. With smokeless loads that cartridge can be loaded down within SASS limits (<1400 ft/sec for rifle and <1000 ft/sec for sixgun). While the M1873 is offered by Uberti in .44 Magnum, for extensive use with magnum loads, I would opt for the M1892, either Winchester (Miroku) or Rossi. The naysayers will tell you that the '92 isn't as "fast" as the '73, but that only matters if you are into real competition mode against the faster shooters. Personally, I shoot Rossi '92's, one chambered in .44-40 and the other in .44 Magnum, with a pair of Old Model Ruger Vaqueros both of which have interchangeable cylinders, one each in each cartridge. Depending on which ammo I currently have, I'll just change cylinders and pick up the matching caliber rifle. I also have matched the two cartridges ballistically with 213 gr. bullets. The .44 Magnum takes LESS powder than the .44-40 because the magnum case has less internal capacity. You can use .44 Special brass in the magnum chambers, but may have some feeding problems in the rifles. Magnum brass works just fine.