I havent opened mine up yet, because I am still learning how to upgrade these types of guns.
I asked barra support for parts diagram, they dont plan on releasing it till they get spare parts available, from what I understand.
Helpful to check out the /airsoft reddit beginners guide and V2 gearbox guide, airsoft GI's youtube channel is another helpful resource to figure out how to dissemble M4 style AEG's. This will help you understand what the parts inside the gearbox do and how different parts have different performance characteristics.
Airsoft parts are kind of hard to figure out what is compatible and what is not. Some upgrades arent plug and play, they require you to do some gunsmithing. If you have a local airsoft shop you can hire a tech to upgrade your gun.
The 400E uses a "version 2" style gearbox which is a style of gearboxes used in M4 style airsoft guns.
You should be able to use V2 gearbox upgrade parts such as different ratio gears, pistons, piston heads, cylinders, motors, springs, and mosfets.
But the barra has proprietary parts such as the inner barrel, nozzle, "hopup" housing and bucking, and Im assuming the tappet plate for the .177 bb instead of 6mm bb.
The top of the gearbox where the upper slides over is bigger than normal V2 gearboxes so some new uppers probably wont fit.
You can use most airsoft furniture compatible with M4 style airsoft guns, but of course depends on the part.
When choosing parts for modding you got to ask yourself what characteristic do you want to change about the gun? Typically when modding AEG's you are choosing between Rate Of Fire or Velocity, unfortunately you cant have both. Some choose a balance between the two, but depends what you want.
Im making a parts list to upgrade my 400E for higher rate of fire and accuracy. Im going to be using 13:1 gear set instead of the stock 30:1,a reduced power spring to get to 250fps, and a mosfet for better trigger and pre-cocking function. This will improve the lock time of the shot and a faster RPM
If you are looking for even more velocity than the stock 380FPS, I wouldn't bother unless you are willing to spend $300-500 on a HPA engine. To get more velocity out of an AEG you would have to put a higher power spring and higher ratio gears, it would increase the lock time a bunch and reduce the full auto RPM.
If you do want to drop the money on a HPA engine and custom parts, it would make for one hell of a build, something that would fill the gap in the market for high velocity HPA BB machine guns that the Drozd left. The HPA engine would allow you to have higher velocities and high RPM's.
Good Luck on the modding!
