One thing to consider when reloading the same caliber for smokeless and black powder.
For best results, use a soft lead bullet with black powder; certainly no harder than wheelweights. And a black powder type lubricant such as SPG or Lyman Black Powder Gold must be used on that soft bullet.
Because black powder creates more fouling, you'll want ample lubricant on that bullet too.
This means that modern, soft, swaged bullets such as those made by Speer and Hornady --- even if you lubricate them later with a black powder lubricant --- will almost certainly lead your bore and be inaccurate because they don't carry enough lubricant to keep the black powder fouling soft.
Conversely, for smokeless loads you'll want a bullet at least as hard as wheelweights, lubricated with a smokeless-type lubricant such as an Alox/beeswax blend.
Thus, you'll need to have one type of bullet alloy and lubricant for smokeless, and another for black powder.
If you use a hard bullet lubricated with a smokeless-type lubricant in black powder loads, you'll get a lot of leading of the bore and accuracy will be lousy.
If you use a soft lead bullet and blackpowder-type lubricant over smokeless powder, you'll get leading and accuracy will be lousy.
This is my experience from over 30 years of shooting the .45 Long Colt in a Ruger Blackhawk, and five years of shooting a .44-40 rifle.
I use Winchester WLP primers in both the .45 Colt and .44-40 for both types of loads. Yep, .44-40 brass is designed to accomodate a pistol primer, even if it's assembled for use in a rifle.
A rifle primer in a .44-40 case will almost always fail to seat flush, as it should be.
I think a .45 Long Colt would be a good choice. The .44-40 has a very limited bullet selection, generally of 200 to 215 grains.
With smokeless powder, you can load the .45 Colt with everything from the 185 grain semi-wadcutter intended for target shooting with the .45 Auto to 300 gr. bullets meant for hunting.
Dan Chamberlain is right. Right after shooting black powder, you'll need to deprime your brass and scrub it clean in hot, soapy water. Then, you'll need to dry it in a pan in a warm (150 degrees or less) oven to chase all the moisture out.
Shooting black powder cartridges is a lot of fun but it's work too.
I avoid the middleman by shooting cap and ball revolvers!