It’s actually a replica of their 22 Long rifle gun they used to make. I wasn’t crazy about the appearance either but got one for a real good price and once I seen how it shoots I didn’t care anymore. Very accurate.Umarex Makes a few also but are in 17 caliber. Theirs has a little plate or lever underneath the grips that you just push up and it Pierces the cartridge.I have the Walther CP 88 that they make that works like that. But they are way under powered for what you need. You’re gonna have to not worry about looks and find some thing that works.Did you look at the other Crosman Guns?Mark 1 that looks like a German Luger .They made a few guns that had a Plunger on them. But through the years they changed some of them on how you pierced the cartridges.
Only the early S&W's had adjustable triggers. They're the good ones. The Mk1's copied the Mk1's. Ruger Mk1 that is. Lol! Get one with the adjustable trigger. Some don't have it. Ok if there is a hole drilled and tapped for a set screw. Just add it. Some aren't drilled. Any Crosman Co2 pistol with a screw on cap will work. Just don't screw it down all the way until you need it. Crosman 150's shoot really well. Even better if you drill and tap a hole in front of the trigger guard to allow a set screw to remove most of the creep in the trigger. Greatly improves the trigger. Only issue is now the safety can't engage. Doesn't bother me especially with a single shot that can also be uncocked easily.
How big are your mongeese? A mongoose is a rodent?
Mongeese?