Camp 9, Camp 45
Both carbines are lots of fun. I bought a Camp 9 new some years ago - when they were still making them, and a Camp 45 a couple years ago in almost new condition.
They're both worth the better part of $500 if you can find one around here.
The recoil buffer will, as pointed out, disintegrate, but you can get one that will last from one of a couple makers of aftermarket buffers - I don't recall the name but you can google "camp9 buffer" or something.
The recoil spring is also, as pointed out, too weak, and if left there, will beat that original buffer to death - get the 23 pound spring from Wolff for either model.
I think these carbines are very like a "big boy's 10/22." They're very handy, reasonably accurate, and fun. I have a 2x red dot sight on mine, which makes for a very good 50-yard varmint gun. Even with a 23 pound spring, they will cycle light loads - this proves to me that the factory spring was WAY too light. It's a great "truck carbine," and is simply limited to what you can expect from a 9mm or 45 slug. Remember that nobody laughs at an Uzi or a Thompson submachinegun. The camp 9 mag is the same as a S&W M59 mag, the 45 uses a M1911 mag, so you can go "extended capacity" in either without breaking your budget.
Good luck finding 'em, boys - they're worth having. I'm not entirely sure I'd want one as a duty gun - only because I have to wonder if it really needs a recoil buffer and spring right "out of the 'chute," what else? I'd rather have something that was "battlefield tested" for that purpose.