I got a Marlin Camp 9 recently for a very good price ($230). Since it was just a "fun" purchase and the price diff between it and the PC9 is rather substantial, the camp got the nod.
I like it a lot. My boys really have a ball with it. Like Chad said, a .22 on steriods.
Its a fun gun, but I don't know that I'd recommend it for home defense, if that's what you have in mind.
It has "stovepiped" (I think that's the right term) several times -- with cheapo CCI ammo I think -- but then, I haven't cleaned it since I got it (couldn't wait)! However, it didn't have that problem with the cheapo Lawman ammo I tried recently.
One thing, though: the guy I bought the gun from said he got a good deal from his distributors because Marlin was discontinuing the Camp carbines. I had heard that rumor at a gun show before he told me but I didn't know if it was true or not. Still don't, actually. Just thought you'd like to know.
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Wound ballistics is the study of effects on the body produced by penetrating projectiles:
Wound Ballistics
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Daily Commentary