A rifle includes a magazine well, a barrel, an exo-bolt, and a rear magazine support. The barrel is detachably coupled to the magazine well. The barrel includes a forward barrel portion on an end of the barrel opposite the magazine well. The exo-bolt is configured to travel along an exterior of the barrel. The rear magazine support is coupled to the magazine well and opposite the barrel. The rear magazine support is configured to come forward toward the barrel and be secured in a plurality of distances from the barrel to adjust a length of the magazine well.