The revolvers generally are grooved for a SHILLING. This made a lot of sense in a day when men were paid a shilling a day, plus found.
I suppose the very rich could use a Sovereign (same size: diameter of a quarter).
The super-rich ones then could throw the Sovereign away. It's only a fifth of an ounce of gold, anyway.
Grooves on the Enfield are a bit wider and they can be undone with an old-style brass THREEPENNY BIT, which was the same size as our Nickel and almost twice as thick.
Webleys used the same system, but the screw came all the way OUT. On the Enfield revolver, the same basic system is used but the screw is supposed to be captive and you only have to back it off enough to let the arm swing. On the Webleys, the screw had to come OUT in order to allow the arm to swing. Either way, careful you don't lose it: replacements are SERIOUSLY hard to find.
Hope this helps.
.