On the Snider Rifle Mark III, the number on the bottom of the Block matches the number of the Rifle, which is stamped UNDER the Barrel.
There were NINE different Marks of Snider ammunition approved in just FIVE years. They had troubles because they were trying to use MUZZLELOADER SOLUTIONS to BREECHLOADER PROBLEMS. Get a cheap Lee Minie mould, the .578" oversize one ($25 from Factory Sales) and machine off the Cone which gives you your Minie hollowbase. You now have a mould for a FLATBASE bullet which, although very heavy, shoots accurately in many rifles.
With the approved 70-grain charge of RFG Number 2 (Black) powder, the 480-grain bullet left the Snider Rifle at 1240 ft/sec, these figures from the TEXT BOOK OF SMALL ARMS - 1909 (HM Stationery Office, London, 1909).
LEE Precision makes a good set of Snider dies and a huge press to handle them.
Will Bilozir (at bilozir.net) goes to most of the gun shows in Western Canada. He has Fiocchi 24-gauge composite (brass and plastic) casings which take our primers and he also handles the Magtech 24-bore brass casings.
FORGET any idea of using 28-bore cases!!!!!!!! We tried that here, some years ago. Everything went peachy-keen and dandy until the Rifle decided to try to go FULL-AUTO on us! Breech-block flipped OPEN while a round was actually FIRIN

case ejected vertically and the Shooter was blasted with very hot Powder Gas. Fortunately, he was wearing glasses with specially hardened lenses, so it cost him "only" $420 and a lot of tiny but painful burns on his face. It COULD have cost his EYES! Be warned!!!!!! NO 28-bore in the Snider!
Otherwise, happy Snidering! The Snider was the FIRST centrefire military rifle in the world using self-contained ammunition: ALL OTHERS descend from it. It was also the first rifle used by Canada as our official Militia rifle and we used them long after everyone else threw them away: into the 1920s as cadet Carbines. They were a single-shot which was engineered well enough that they could be fired 18 round per minute: I have actually done this. And there is absolutely NUTHIN' as much fun on a range on a warm Summer day.
Hope this helps.