The gearbox is the engine of an electric gun, and learning to work on it is a rite of passage for any serious airsoft tech. Whether you are swapping a spring to hit a site FPS limit, replacing a worn piston, or building a gearbox for speed or torque, quality internals are what make an AEG reliable and tuned to your needs.
We stock airsoft gearbox internals from trusted names like ZCI, Action Army, Rocket Airsoft, ASG, and Unicorn, including pistons, springs, gears, tappet plates, and more. Browse the range below and build the gearbox you want.
Inside every electric gun, the gearbox turns battery power into a shot. The motor spins a set of gears that pull back a piston against a spring, then release it to fire a blast of air that propels the BB. Every part in that cycle works hard, and the weakest component is usually the first to fail. Upgrading to stronger internals improves both reliability and performance, which is why teching a gearbox is such a core part of the hobby.
The single biggest factor in your FPS is the main spring, and it is the part you are most likely to change. Springs are rated by power, such as M100, M120, or M140, with a higher number meaning a stronger spring and higher FPS. Swapping the spring is the standard way to bring a gun to a site-legal velocity, and we stock a full range including Action Army and Unicorn non-linear springs.
Always rechronograph after a spring change to confirm your FPS, and remember that a stronger spring puts more stress on the rest of the gearbox, so pair it with suitably robust internals.
The piston takes a beating every shot, so a reinforced piston with steel or polycarbonate teeth, like the ZCI and Rocket Airsoft pistons, is a popular reliability upgrade. The tappet plate times the feeding of BBs and is a common wear part, while quality gears ensure smooth, durable power transfer. Build these together as a matched set and you get a gearbox that is far tougher than stock and tuned to your chosen balance of speed and power.
For the guns these go in, see our electric AEG rifles, and pair your build with mosfets and electronics for the best trigger response.
The main spring controls FPS, so changing it is how you adjust velocity. Springs are rated by power, like M100 for lower FPS or M120 and up for higher, so fit a spring rated for your target velocity. Always rechronograph after the change to confirm you are within your site’s limit, and pair stronger springs with reinforced internals.
A reinforced piston with steel or polycarbonate teeth is one of the best reliability upgrades, as the piston is a common failure point. Quality gears, a good tappet plate, and correct shimming also make a big difference. Building these as a matched set, rather than upgrading one part in isolation, gives the most reliable gearbox.
Gearbox work is more involved than external upgrades, but it is very achievable with patience, the right tools, and a good guide. Many players learn on a spare gearbox first. If you are not confident, start with simpler upgrades like hop and barrel parts, and our tech team can handle gearbox work for you if needed.
