For what it's worth, I played with a baby rolling-block as my main match rifle for a season. I was doing a Navy impression that year, and the baby rolling block, in .45 Colt, was the closest I could get to a Navy carbine, although not in the original's .50 calibre, nor barrel length.
It was great fun, and really kept me on the ball as far as maintaining target order awareness. Trick was to not drop it from your shoulder too far when working the action and gently "ram" each cartridge up to, but not past, the rim extractor. I loaded the loose rounds from a CW pistol cartridge box on my belt.
Drawback was, though I felt I was getting fairly fast once I got into the rhythm, I had one club send me a hatchet letter requesting I don't come back with it. The accusation was I was trying to slow their match down.
RCJ