Strange MP5 Double Feeding

[midnight_commander]

I built an MP5 out of a bunch of spare parts I had in my tool kit, but it seems to have this strange double feed issue.

It shoots fine occasionally, but other times it seems like the motor almost cycles an extra half cycle or something thus putting two BBs into the chamber before firing resulting in two BBs coming out of the barrel.

Originally I think I had a bad motor on it because the sound was very apparent. You would hear the piston head hit the cylinder head, then you would hear the piston cycle half way again.

After I changed the motor this seemed to get better, but I looked at air nozzle while cycling the gearbox and it seems to be moving in and out twice thus feeding two BBs into the hopup.

This is the first time this has happened to me, and after attempting to trouble shoot for at least 20 hours I've given up and decided to consult the experts.

Has anyone had this trouble before, and know a remedy?

EDIT: My bevel gear only has 4 notches on it, and it sounds like it might be back pedaling when it cycles. Is the only remedy to get a new bevel gear?

EDIT 2: Maybe Improper gear timing, I timed it so that the notch on the sector gear was in the one o'clock position. Is this incorrect?

[Cap n pickles]

The bevel gear timing is fine, that gear spins so fast that it only needs 4 slots.

Are you using the correct Nozzle for it? maybe in your spare parts you put in the wrong nozzle?

Does it make a noisy grind sound?

Is the tappet plate broke?

Maybe the Hop up unit is not exactly compatible with the gun (Assuming its from another gun?)

The Bucking could be worn down, and is letting the gun Double feed.

Your right about the 1 o'clock position hitting, i have bad double feeds in my AK's (Mostly with a HICAP) if i don't set it to 1.

Try all these, Inspect, and T&E. If you still cant get it to work, Phoenix, or Myself wouldn't mind looking into it.

I say try the bucking, replace it.