Stop in for a cup of coffee

So today I was cleaning and organizing the cabinets in the garage, and I found this.
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Apparently my dad got it when he was driving long haul big rig from the middle of nowhere to vegas and truck robberies were common. (I don't think it was ever used like that, probably only messing around target practice after he quit that company) I want to try and get it going again and I know there are a few people on here that have experience with firearms and might have a clue how to get this working.
(it does cycle good, nothing is locked up, but before I try and buy Co2 and fire it I wanted people's opinons)