Airsoft M249 gearbox shell for HPA

A printable, lighter gearbox shell for your airsoft M249, for use with an HPA engine. Tested with CA, should fit A&K too.

I used a Digispark “arduino-style” board as an FCU along with an IRF520 breakout board, but the design should allow for plenty of options. I've also added multiple holes to finetune the placement of your microswitch for the trigger system. 

Bolts for the gearbox are M3; uses stock (M5?) bolts to mount to the receiver.

Included is a small Arduino sketch as well to function as an FCU. It's quick, dirty and blocking code, but it works.

Tested to fit in my Classic Army M249 Para along with a Wolverine Reaper.