Kel Tec SU18 C will fit in a tennis racquet case and takes regular AR1`5 mags, weighs, well here are the stats and one was on here (ODT) Tuesday for $450, and they can be fired in folder position. I have one that is as accurate as an AR at 100 yards.
Calibers: .223 Rem 5.56mm
Weight unloaded: 4.7lbs. 2.1kg
Length: 35.5" 901.7mm
Length Folded: 25.5" 647.7mm
Barrel length: 16.0" 406.4mm
Magazine Capacity: 10 rounds, or M-16 compatible
Twist: 1:9" 1:228.6mm
Trigger Pull: 5lbs to 7lbs 22.2N to
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I have an SU-16b in a tennis raquet bag. Front pocket holds several mags plus 2@10 rounds each that store in the butt stock but that rascal in the machete sheath is hard to beat for a backpackin rifle that can feed you