From what I understand, cut down .45 Colt cases will work in an un-shaved Webley. I like the AR cases which look really cool with the long nose 265 grain Webley bullet seated in it.
Cut down 45 Colt case wouldn't work in un-shaved Webley Mk VI, unless revolver is out of specification. See:
Also, in my experience, 45 Colt cases are not good choice for making Webley brass, at least using Starline brass. I was making Mk I version, and after reducing length, I had to ream case about .400 deep. Starline 45 Schofield brass is OK, no reaming was required, just shortening. The best option is to use straight 45 Cowboy Special brass
https://www.starlinebrass.com/45-cowboy-special , length is OK as is. Now, the issue is rim thinning. It could be done on lathe, but I found better way. Here is the tool I created:
For the best results use tool steel and heat threat parts.
A good, strong milling machining vise is more than enough. Smaller hydraulic press should be fine also. Caution when thinning rim on case made from 45 Schofield brass; you will find that rim grew in diameter bit more than expected, so it could have quite tight fit in shellholder. Try to turn it until fits in the slot. Better yet, make that rim formation space .040", instead .038".
My apology for off topic, I just wanted to clarify few things and save Webley enthusiasts from aggravation and high cost.