Apologies for reviving a dormant thread, but new information has come to light (to me, anyway) about the use of nitrocellulose powder, or gun-cotton, in pin-fire game guns, long before the Proof Houses deemed to change the rules on the subject in 1896.

Gun-cotton in sporting guns was used as early as 1856, and commercial gun-cotton cartridges were used from 1863 onwards. You can read about it here, in the latest issue of The Vintage Gun Journal.