Apart from the trigger and pistol grip, one of the most actively used part of a gun is the rear butt stock. Often it would be braced and seated against you to help you get into an optimal firing position and not something overlooked by engineers and shooters alike. With airsoft a change of the butt stock can open new options for you. If you're done with jamming your airsoft gun's battery into the hand guard, wiring the gun to the rear and installing a full stock would allow to easily fit a battery into is spacious compartment. Crane stocks allow for the fitment of special crane type batteries while others features sling points, enhanced rubber butt pads, and extra compartments.