I bought a pistol caliber carbine a while back, it's a KelTec Sub 2000 in 9mm. They accept Glock mags so I picked up some 30 round happy sticks to go with it.
Some people will knock KelTec, but from my own experience they are top notch when it comes to customer service and standing behind what they make.
This thing is pretty decent out to 100 yards, and I have hit the steel at 200 yards.
Nice because it fits in a back pack with ease. Makes a great "truck gun".