Longknife 76,
I don't think m-g Willy was worried about the rear of the cylinder failing, but rather higher pressure ejecting a much larger volume of gasses through the nipple.
When a friend and I first started using Triple 7 in our cap and ball revolvers, we liked it in our 1851s, 1860s, 1858s, etc. but found out the Dragoons and Walkers can be overloaded with it. He loaded his Uberti Dragoon full, and I my old ASM Walker. He went first, and after the first shot, turned and remarked that for the first time he had experienced "real" recoil from a cap and ball revolver.
After the second shot, he stepped back, and started rubbing his face. The escaping gasses had blown the hammer back to half cock, and unlocked the cylinder. Cap fragments had hit him in the face with enough force to draw a little blood in three places. It may have partly been the fault of an erroded touch hole, but we use only genuine black in the big revolvers since this little lesson.
If the extra pressure of 777 can do that, I don't even want to be around when someone uses smokeless with nipples and caps !!!!