All-Round Build Kit for M4 AEG (V2 Gearbox)

The All-Round Build Kit is our take on a complete upgrade for M4 AEGs with a standard V2 gearbox. The kit brings together the parts that genuinely move performance in a standard AEG: gear set, motor, piston, piston head, cylinder head, spring guide and spring. They are chosen to work together as one setup, not just as individual parts. The result is an AEG with fast semi-auto response, a rate of fire of around 21 rounds per second on an 11.1 V battery with the brushed motor, and a gearbox built to last through many game days.

Many players upgrade an AEG by buying the most expensive part in each category, and that rarely gives the best gun. A motor that is too fast on the wrong gear set needs high-speed modifications, draws more current and wears the gearbox harder. The All-Round build goes the other way: the balance between gearing, motor and spring force is set for the way most people actually play – mainly semi and short bursts. You can fit the kit yourself, or let our workshop assemble, shim and test it.

A well-matched setup, durable materials and free choice of spring

The parts are chosen to complement each other and need no further special adjustment:

• Gear set in the 16:1 class: A mid ratio that gives faster cycling than the standard 18:1 without needing the high-speed modifications that 12:1 and 13:1 typically do. It strikes a good balance between response and load on motor and battery.
• Piston with 14-tooth metal rack: The body is PA66 polymer, and the tooth rack is metal all the way. The 14th tooth is matched to the sector gear's engagement (AOE), so the cycle becomes more consistent. An all-plastic piston is the typical weak point in a standard gearbox when spring force goes up.
• Aluminium cylinder head with thick pad: CNC-machined aluminium with a rubber pad twice as thick as normal. The pad absorbs the piston head's impact, so less of the energy is passed on to the gearbox shell.
• Brushed or brushless motor: The standard variant uses a high-torque brushed motor matched to the gearing. The brushless variant uses our own HT Brushless 39K, which can be set to 31,000 or 39,000 RPM. There are no brushes to wear, and efficiency is higher. If your gun doesn't already have a MOSFET/ETU, you can add one: the E-Shooter Kestrel V2, which can be set up from an app, the Jefftron Scylla V2, or the Jefftron Leviathan V2, the premium version supplied with its own trigger.
• Free choice of spring from M100 to M130: You choose the spring based on the site you play at. The whole build is matched to this range, so you can change spring later without rebuilding.

Maintenance and safety

• Fitting requires disassembly of the gearbox, shimming and correct lubrication. If you haven't done it before, we recommend having it fitted in our workshop
• Always measure velocity with a chronograph after fitting, and stay within the site's limits for your type of replica
• Use an 11.1 V LiPo battery with a suitable discharge rating, and always charge with a balance charger in a LiPo safety bag
• Clean the barrel and hop-up regularly, and inspect the gearbox after a season with many game days
• Always wear approved eye protection during play and testing