I’ve been messing around with loads for .38 S&W (NOT .38 Special, it’s a different cartridge) and trying to make sense of the contradictory and sometimes unhelpful advice from Americans on the subject.
Anyway, it turns out 3.2gr of Unique behind a 145gr LRN projectile does not work well at all out of a Webley Mk IV. It goes bang, but is incredibly inaccurate - despite being a promising load “on screen”.
Might try a heavier cartridge next time - I hear 158gr projectiles can work quite well.
Please do keep us updated on this. A Webley is definitely on my shopping list.
@bentaz on your list? I have brass and stuff for you than… Don’t buy any reloading stuff for it.
Yours is 455 isn’t, or wasn’t it?
I want one of them too, but not able to get High Cal permit just yet.
Why not.
You should find somewhere that shoots Metallic Silhouette and get that .45 endorsement. Then get a Mk VI Webley in .455. Then use it to shoot the matches, and have fun while the people with customised guns still don’t score much better (or better at all) than you. 
Stupid NSW laws say I need full Cat-H for 12 months before I’m able to apply for a high Cal permit.
Ok, so very soon than, very good.
In time for Xmas I believe, coz it was Christmas when I bought my first pistol (3rd) on my full licence.