If it was mine I would be making the claim and just provide a qualification that you are 90% sure, in the absence of any conflicting information. I would be saying "it is believed to be a rifle owned by Col Gordon, the famous Gordon of Khartoum."

Colonels are not so common, that numerous "Col Gordon" would have existed in that same year. Of course possible, but you may never actually prove his ownership 100%.

As far as I know, he wasn't a celebrated hunter, but military leader, adventurer and leader, s a sporting arm, a necessity for any senior officer, may not have been a big thing in his career and life. If it sat in Scotland, maybe only rare use when "home".

A nice treasure for the wall and occasional use.