Curl:
There are a couple of very comprehensive books, though out-of-print now and probably expensive: "The Webley Story" by Bill Dowell, and "Webley Revolvers" by Gordon Bruce & Christian Reinhart. The second is a modern revision of the first, but quite different in layout. Skennerton's 'Small Arms Identification Series' on the Mk.VI is a gem, and there have been some marvellous articles in the British gun press over the years.

There may also be a good website, I'll see what I can find.

The only criticism I have of the Mk.VI is a heavy trigger-pull, especially in one-handed double-action shooting.

I've seen the .45 ACP conversions and the half-moon clips, but never fired one. The .455 ammo is easy to reload, I use green-moly deep-hollow-base projectiles swaged by WestCasting, but have to cannelure the bullet to permit crimping or they creep out during firing. Built my own cannelure tool for this.

9Three:
Never heard of the condition you describe in a Webley revolver. I shoot nearly all of mine, especially the Mk.II and Mk.VI .455s and none of them drop to half-cock.

That would be bloody annoying!