Not big in the BP thing, but still, probably the most important thing would be the twist rate for the bullets being used.
In a standard rifle, the faster the twist, the heavier for caliber bullets you can use. This said, velocity has some to do with that as well.
I think that the diameter/length of these BP bullets however will require a slower twist as they are heavier bur fatter in diameter. So, I would think with the standard 45 caliber barrel, the twist would be more suited to the bullet weights it normally shoots and the same for the 50, but when you sabot the 50 your going to or should be able to run it a bit faster to make up for the slower twist. If that makes any sense to you. Bottom line is you would probably have to try out the combination in each to determine the actual best of the two in accuracy at that specific range.
So all that said, I'm just as confused now as I was when I started typing. LOL Hope it helped some,
So many variables..... hard to say. you can probably get either of them to shoot with some work, testing, etc.
Remember, one of the reasons modern smokeless is more accurate than blackpoweder is because of consistency. Weigh your bullets/balls, weigh your powder charges accurately (I've never used the pellets so I am not sure how consistent they are), and be consistent every time during your loading/firing process and in your cleaning and maintenance.
Also, as SC mentioned above, know what your weapon was rifled for. Balls and bullets need different twists. The difference between sabots and bullets shouldn't be as great but I am sure there is one. Find out what the manufacturer recommends.
I'm going back up prob. thur. will shoot both and let know! I'm using 150 grains peridex pellets in both. 50 with 45 sabot and 45 with 45 both bullets are hornady xtp i think. let yall know about tues after hunting