True, I do have to pay a steep price for my #2 Musket cases, unfortunately - but hey, if you want to be exclusive...
A deeley & Edge or a Fraser sidelever would be neat, even a Field (a bit more affordable too). Good thing is - for anything WR you could use #2 Musket, and yoo could use the long .50 case as basic brass. After all, you will need a custom reamer...
My 2nd Match rifle in #2 Musket is already shootable - Westley Richards ZAR Martini action, 1:16" Metford early style rifling in a 33 1/4" barrel. Metalwork is done, now for the wood and the finish...