A picture of the proof marks could quickly narrow it down to when the gun was proofed. Records tend to be harder or non existent for many makers. Another clue could be any address on the rib as many makers/retailers moved around or more often street names got changed. So a rib marked Bridge street might denote an address that maker was known to have been located at from1890-1896. So even if no factory books, ledgers or records it still might be possible to narrow things down.