The m249 gearbox
This gearbox is only used in m249 style LMG's. The gearbox is a modified version 2 gearbox, so some version 2 gearbox parts work with this box. But it also suffers from some problems, bur more about that later.
Remove the spring.
The first cool feature you will notice on this gearbox, is that it has a cleaver "Quick spring change" feature. What you do is press the back round spring guide, forward a bit with your finger. Then release the small gripping arm that holds the spring guide. Then the whole spring guide and spring can be pulled out of the back.
Open the box.
Then remove the 12 screws that clamps the gearbox half’s together. And pop the gearbox open.
With the gearbox split in 2 you can see all the parts. And notice that the motor (Short version motor) is placed inside the gearbox housing itself. Both: Gears, Cylinder and head, piston and head, and nozzle guide are the same as version 2. So there’s allot of parts that fit's this box.
On this version box the trigger is not the same as any other box. It's an electric trigger, where a small metal leaver presses 2 metal parts together. This is both smart and stupid at the same time. The smart thing is that the trigger is a small 3$ part so if it burns off then you can just replace it. Now that's nice! Especially on a gun that only shoots on full auto, and has a 2500 bb mag attached. And lots of shooting men’s lots of burns on the trigger.
Problem: The electrical trigger has one problem. If you pull allot of amps over the trigger then the metal part burns stuck together, leaving you unable to make the gun stop shooting! Now that’s a BIG problem, especially when the battery is hidden inside the gun so you can't disconnect it.
Solution: Get a mosfet -> So that the trigger don't burn.
Disassembly: The trigger housing is made of 2 parts that can simply be pulled apart.
It's a nice easy box to work with, but I highly recommend to get a mosfet on the box. I know that most of the m249's only gets to shoot 10-20.000 bb's before the contacts start acting up, so get a mosfet before you get into problems. Also be aware that the stronger spring the box has the bigger the problem will be, so don’t upgrade the spring before you have a mosfet system.
Easy wo work on, and easy to upgrade, just fix the trigger problem first.