The most common method is bullpup rifles. Moving the barrel back into the buttstock while the trigger mechanism is kept in the same place.
Crossed Ar15 Clip Art At Clker Com Vector Clip Art Online Royalty
ICS-190 GLM multi shot 40mm airsoft grenade launcher - $135.80
CZ 91364 805 Bren S1 Carbine AR Pistol Semi-Automatic 300 AAC Blackout/Whisper (7.62x35mm) 11″ 30+1 Flat Dark Earth