I found this in the yard of a house I used to live, it was an extremely old farmhouse that they have now torn down. Me and my sister were looking where our tire swing and woods were. I have no clue what it is, and I don't think it came from my family when we lived there. It was about 5 inches down.
That’s what I’m thinking too! We lived there 20 years ago so it could be one of my brothers toy cap gun handles! Pretty cool going up there and maybe finding old things from way back, or things from my family. It’s like a win win!
Without intending to (while researching the current thread about a capgun barrel) I stumbled across one that seems even closer than the very good answer from Icewing. The Kilgore Hawkeye in the link and picture below shows part of the inside, which I think matches the backside of yours, and the cross hatched area is raised slightly like on yours. https://www.gunauction.com/buy/9312874