Angel Custom CNC Machined 8mm Fully Upgraded Gearbox Shell for M249 and Mk46 Airsoft LMGs

"If you own an old A&K or Classic Army M249, this gearbox paired with the Bullgear CNC Hop-up unit is an absolute must have. This gearbox is very good and required very little effort to get running flawlessly. Here is a complete brake down of what to expect.

The gearbox case in extremely high quality and much lighter weight than the stock case.
The gears are high quality 18:1 ratio and seem very durable. I swapped mine out for a high end 19.5:1 gearset only because I had them sitting around.
The shimming was almost perfect. I only changed .1mm on the Bevel Gear to mate up better to the motor pinion. All the other gears were shimmed perfectly.
The AOE was nearly perfect as well which was always a problem on the old A&K/Classic Army M249's. I had to add a .2mm spacer to the piston head to dial in the AOE and I shaved a tiny bit of the second to last tooth on the piston rack to mate up perfectly to the sector gear.
The compression parts are very nice and the air seal was perfect right out of the box. FPS varied less than 2FPS per shot through 50 rounds.
The Air Nozzle is an O-ring type 21.6mm I believe which is slightly longer than stock but this does not matter because it feed perfectly.
The spring guide is a metal ball bearing type and is high quality as well.
The spring seems like a M120 non-linear type. You may want to downgrade to a M110 depending on your field limits. My gearbox shot 320fps with 0.32g bb's so a little hot for a support gun.
The included motor is basically identical to the CYMA high torque that comes with Cyma Platinum airsoft guns. It is a good motor with a fast ROF.
The wiring is decent but I swapped it out for my GATE Nano wiring harness.

The only issue I found with this gearbox was with the motor adjustment screw. When shooting full auto, the motor adjustment screw will slowly back itself out. This can be remedied with a tiny bit of Loctite after you have the adjustment dialed in. With that said, the motor mine came with was dialed in perfectly with the adjustment screw out all the way so this was a non issue for me. If you plan on swapping motors out, because every motor will have slightly different shaft lengths, you will probably need to Loctite the adjustment screw in place once it is adjusted.

"Nothing bad to say, very good internals although you get basically the same performance as the stock gearbox. I put in a better motor, dropped in a higher gearset and ditched the wiring in favor of the stock wiring & it's been performing reliably at 30rps+ for over a year of continued use.