It looks like a very old/early air rifle, like a Diana Gem, but the Gems don't have the piston cylinder going all the way to the toe of the gun. It is actually a bullpup air rifle. Agree don't rush into cleaning it up.
Anyway... at least found an interesting airgun story on my trawl for early air guns:
https://www.dailymail.co.uk/news/art...mily-home.html
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