Agree - bite the bullet, buy a couple hundred rounds of Fiocchi and never look back.
I found myself in this dilemma; collected as much brass as I could get and ended-up with a couple of boxes of weirdos and a whole lot of finickin'. Here's what I ended-up with:
100 rds of Fiocchi - 455 shellholder, small primers
~50 rounds of Hornady, plus a couple-odd rounds of D.C.Co 455 Colt; 455 shellholder, large primers
~100 rounds of cut-down .45 Long Colt; .45 LC shellholder, large primers.
And if you're making .455 out of .45 LC, they will not stay in the 455 shellholder (I tried) and you have to thin the rim (on a lathe or drill press, cutting from the cartridge-side because if you cut from the bottom you'll shorten the primer pocket). This is a must-do step, my Webley will not turn the cylinder if the rim is too thick. So you'll save yourself massive bother by just buying 300 rds of Fiocchi; they'll all fit and you'll only need one size of primer.
Your alternative is to find yourself an extra cut-down cylinder (it takes literally 30 seconds and a big coin to swap them) and shoot .45 Auto Rim, or .45 ACP with moon clips BUT!!! if you're shooting .45 ACP in a Webley, DO NOT use store-bought, and load yours very soft - Webleys will burst if you feed 'em too-hot .45 ACP's. I bought a spare cut-down cylinder for mine; standard load is a 230gr lead TC (Lee sells a 6-cavity mould) with 3.5gr Trail Boss; gives ~620 f/s and both our .45's will shoot this load well and cycle it. I've seen no load data for the Webley, but it hurts my knuckles against the back of the trigger guard with this load, and I'm shooting a 35gr lighter bullet 100 f/s slower than the stock Webley load, so I figger I'm pretty safe.
- and, enjoy the h@ck out of it!