Thanks for your comments, gentlemen!

Fired 38 special cases measure approximately .378" OD diameter after shooting, and a chamber cast would indicate this to be a .360 #5 Rook.

I've received two suggestions for bullets:

- 'bumping up' a .358 HBWC by squeezing longitudinally in a vice.

- trying a cast .36 conical bullet of .375 diameter that has a smaller diameter base (Lee Precision mould)

I may consider a custom mould if these suggestions are unsatisfactory.

I've ordered a copy of Winfer's BRITISH SINGLE SHOT RIFLES, VOLUME 7: ROOK, RABBIT & MINIATURE RIFLES; perhaps that will help in the search to discover the maker.

Cheers!

mbatten