After that you should have everything in place and can begin adding the screws to the gearbox. The best idea is to start with the center screw and work your way outward.

Once that's done you can begin going threw and checking a few parts to be sure everything is done correctly.

First check the piston by repeating step 6. This done for a few reasons

First to make sure the piston is properly in place because that doesn't always prevent the gearbox from fitting together

Second if you are using a piston from a different manufacturer some brand can be way to fat and will be dragging on the sides of the gearbox when moving back and forth. This will cause low velocity and catastrophic failure of both the piston and over time the gears.

Now Check the air-nozzle and tappet plate by gently grabbing the air-nozzle by pushing it easily back and letting go. It should spring back into position quickly and smoothly.

If it does not function properly do not force it as this could damage parts. This could be a result of improper installation or a bad fit if you are using a non-G&G air-nozzle and or tappet plate.