mr.rideout:
Metallurgy in the early part of the 20th century was not what it is today. "Nitro-proofed" handguns may have only barely survived the proofing process. Most ammunition of that time was also lead bullets unless of military caliber. Your MkVI Webley was proofed for the .455 Webley cartridge (12K psi) and should be OK with modern made .455 Webley ammo if you can find any. Many of them were converted to fire American .45 ACP cartridges that are really too powerful (20K psi) and will eventually damage your gun. "Velo-style" .32 long Colt originally had a "heeled" lead bullet and was quite different from the .32 S&W long cartridge. Both were loaded to black powder pressure levels before 1920.
I too like and shoot early 20th century revolvers, but I handload them with lead bullets and keep pressures down to black powder equivalent and avoid really fast burning powders (like Trail Boss, Bullseye, Vihta Vuori N310, Red Dot, etc.) where an extra 10th of a grain will be an overload. You really can't go wrong using real black powder either. I load for .32 S&W, .32 S&W long, .38 Short Colt, .,38 long Colt, .38 S&W, and .45 Adams, all top break revolvers made before 1920 using both real black powder and light loads of smokeless powder (individually weighed charges!) These guns can be fun to shoot if you are careful and respect their limits.