Have you forgot about the Gem repeater?, isn't this similar?..
Hi Dave. No, I remembered that one, but assumed it involved balls dropping straight into the breach (I must confess I didn't totally understand your detailed explanation ). I was thinking about the Girandoni's sliding breach really.
Vintage Airguns Gallery
..Above link posted with permission from Gareth W-B In British slang an anorak is a person who has a very strong interest in niche subjects.