Yes: to clarify, .45 Auto Rim brass is made with a very thick rim which has the same effective thickness as the .45ACP brass in a moon clip - i.e. designed to be used "loose" in a revolver manufactured (or "shaved") for use with .45ACP and moon clips.
Using .45AR brass permits the revolver to be "properly" loaded with individual rounds, and is the only way to get the incredibly satisfying "flock extraction" of a break-top Webley revolver ...
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All of my various .455 revolvers are in original configuration, so I wouldn't dream of honing out the chamber mouths ... rather, I use the 265gr hollow base bullets of original shape that those tight throats were designed for ....
I would strongly recommend using .455 Webley dies to reload your brass, because after your brass (either .45ACP or .45AR) has been fired once in your Webley chamber, it will be fireformed to the more generous diameters of the Webley cartridge/chamber. .455 dies will only size the brass back down to .455 specs ... .45 Colt and.45ACPdies will size it down to the slightly smaller diameters of those cartridges with every loading, but it will blow back out to the more generous Webley diameters with each firing, so you'll "overwork" your brass over time ...
Chuck will be better able to address this: I don't know how GAF rules would treat the use of moon clips in actual competition with a Webley revolver ... at least in main-match events ... because they are certainly not "period correct" for a Webley and would in fact give an unfair (in my mind, at any rate) speed advantage over a similar revolver being loaded with loose cartridges. As I recall, such "loading aids" are not permitted ... except perhaps in "Era of Expansion" side matches, where I have been permittted to use my period-correct Prideaux Loaders ...