Long ago, back when Bullseye was still made by Hercules, I experimented with smokeless loads for the Ruger Old Army.
I used weighed charges known to be safe in cartridge .45 revolvers behind .457 roundballs.
I did not seat the ball on the powder but only flush with the chamber mouth, much like a cartridge would be loaded.
The first thing I learned was that #11 percussion caps on a standard nipple would not reliably ignite smokeless and when it did, it resulted in a squib load.
Then I added a very small amount of FFFFg to act as an igniter, essentially doing the job of a modern primer.
This worked and I shot several cylinders using this load, but since the small amount of black powder booster still left me with a revolver to clean, I did not see the point of going further and quit doing it.
It seems that the primer in a modern smokeless load has to do more than just ignite the powder, it is also responsible for getting the initial chamber pressure high enough to get the smokeless powder into its fast burning mode. If you simply set the charge on fire, you usually get a squib, and that may fool someone into thinking the charge needs to be increased. So someone increases the charge until there is enough powder in there for it to burn into its fast burning pressure threshold and you go from squib to kaboom.
Backing up my belief that smokeless needs a powerful primer to get the initial chamber pressure up to the fast burn threshold is my informal research in 16 inch guns used on battleships. It seems that between the main charge of about 600 pounds of smokeless powder and the primer goes a 5kg bag of black powder to act as an igniter.
Anyway, in the UK, there is a company called Westlake Engineering that converts modern .357magnum revolvers into smokeless muzzleloading revolvers for the UK market, where cartridge revolvers are extremely restricted. The cylinders on these revolvers are designed to use #209 shotgun primers instead of percussion caps.