The idea that no amount of any kind of black powder is enough to blow up the cylinder is boloney. Someone once burst the cylinder of an ASM Walker using between 40 and 52 grains of 777 3f behind a 280 grain conical designed for the Ruger Old Army.
The one who blew up his walker said he used 30 grains then changed his story to 40 grains (said he made a mistake.) The seller of the projectile said it was 52 grains of powder. Now 40 grains by weight is about 52 grains by volume when using 777 according to a weight chart I read so I don't know if this guy weighed his charge or measured by volume, but it was 3f grade 777 so I don't think 4f would be safe but suffice to say it would all fit in the cylinder.
One guy on youtube loaded up the cylinders of a walker with 60 grains of 4f behind a round ball and shot it with no kabooms but that does not mean it was safe he was chastised by viewers in the comments and he finally agreed, and rightfully so, that what he did was not a good idea.
Granted these are two very different loads with the conical probably producing more pressure but it did all fit into the cylinder and ended up with a kaboom that these kind of ad hock loading practices can produce. Thankfully there were no injuries.
Thompson Center produced a very good instruction manual that provided a comprehensive list of maximum loads and projectile weights for their black powder rifles a lot of which were very powerful loads with heavy projectiles and good range.
They strongly state not to use 3f in the big bore rifles. They have actually researched the matter and found finer granulated powders produce significantly higher pressures than than the coarser powders and (pay really good attention to this) the increase in performance with the finer powders marginal. Thompson Center Made some super strong high quality side locks, that have actually researched the effects of finer powders and don't believe anything finer than 2f is safe in their large bore rifles or performs significantly better than their already super stout recommended 2f powder loads with heavy projectiles.
I am sure a 3f load can be safely when used in proper doses and many people routinely use 3f in TC as well as other side locks but I don't because I don't need to.
Granted the Italians have their recommended lawyer useless (unless you shoot paper and like low power loads) weak loads for their cap and ball guns but over the years (as far back as the Civil War) a general understanding of what these revolvers are capable of handling is known.
That is a far cry from telling people to just load as much of any grade of black powder into the cylinder behind a projectile of their choosing and not to worry about it.
That is bad advice and I don't think it's a smart thing to do.
Sir I just hope the shrapnel does not fly into you or anyone else.
I have had it here.