I've got a Westley Richards first model in 500/450, 1 1/2" case, .....does anyone have info on this case and loads? Haven't really paid much attention to it as there's lots of provinance, but another showed up today.

There's two types of case for this round, the first which I would discard is the original coiled brass case like the early .577 Snider rounds, the .577/450 
Martini-Henry rifle and many other early British Sporting rounds. The second type is the Drawn Case loads which is what you want to emulate. The following loads are of British origin being made by Eley and/or Kynock, or both.

I give the Black Powder loads only as the early nitro loadings cannot be duplicated as the powders are long out of production.

Eley 25 grns BP, 225grn bullet lead round nose.

Eley 25 grns BP, 225grn bullet lead paper patch round nose hollow point.

Eley 28 grns BP, 214grn bullet lead paper patch round nose hollow point.

Kynock and Eley 28grns BP, 270grn bullet lead paper patch round nose.

Kynock and Eley 28 grns BP, 270grn bullet lead paper patched round nose copper tubed.

Eley and Kynock 28grns BP, 270grn bullet lead round nose copper tubed.

Standard factory ammo so duplication using BP is not too difficult. PP can also be done but you may find copper tube bullets very difficult to obtain. 
Source. British Sporting Rifle Cartridges 1993 by Bill Fleming. A great book but rarer than a live T.Rex. 

Edit: There is a copy of this book for sale on www.abebooks for the miserly sum of US$ 499.95  plus postage.

Harry

Hello Arctic,
Usually on British Rifle rounds when a double figure is used such as .500/.450 it means that an original .500 case has been taken , then necked down and then the surplus brass cut off. I haven't actually checked the cartridge base dimensions but I feel confident that a .500 case will do all you will need is a case forming die.
I understand that there are some companies producing .500 brass. Sadly these large cases are seldom cheap. Try your usual outlets for brass and manufacturers like Starline, Bertram and Kynamco and the larger retailers of brass, Midway, Graf, Buffalo Arms Co. etc. Check the case and rim dimensions in Barnes COW. Brass of all calibres from all manufacturers is hard to find and has been for some considerable time.

Good luck,

Harry