Can't comment on the Cowboy side, but I have shot my lever guns a bit
I have 2 Winchester Trappers, one in .44 Mag and one in .45 LC. The .45 shoots a little "easier". A bit hard to describe, but for some reason the .45 gives more of a push against the shoulder instead of a hard "rap" like the .44. Granted, I have only shot a few (20) rounds through the .45, but I noticed it right away. I handload the .44 to about the same levels as the loads I used in the .45, if anything my handloads were a little less. I also have a Marlin Cowboy II in .357. Of the three, the Marlin is the smoothest, but the hardest to shoot. It takes me 4 to 10 shots to get used to it, but after that it's fine. I think it's because of the buckhorn sight on the Marlin. I like them all equally, for different reasons, but bottom line: If I had to go out and buy just one, I think it would be a Marlin Cowboy II in .45LC. Can't comment on the Rossi since I haven't tried one. Same goes for the 44-40, Haven't tried it yet. Has anybody else noticed the difference between the .44Mag. loaded down and the .45LC or is it just me? If so, does the .44-40 act like the .45LC in that respect?