Kwa M4 not firing
 

Hi guys! I just bought a Kwa M4 and the gun dont shoot the gearbox cycles well but theres is 1 out of 10 bb that come out. I opened the gun noticed that the air nozzle was loose so i opened the gearbox the plastic piston head was broken in half so i took my scar's piston head and put it in the gear box and reassembled everything.I have the same problem...

I think there is more than 1 issue with the gun I think the previous owner broke the pieston head from dry firing. I checked the hop-up unit with a mag and the bb goes trought so i dont think it is a hop-up issue... what do you guys think?

Update: After many disassembly and reassembly The gear box seem to work fine i reassembled the gun and still no bb come out. I tried with magpul mags and the stock kwa mag and still nothing the gearbox cycles fine and no bb comme out.

If the gearbox works fine, problem must be with your hopup, or mag.
Test the mag to see if BBs are coming out properly. If they stay in when the release is depressed or fall out slowly you will need to look at your mag.
If mag is fine, check your hopup, the dial may be set too high, the bucking could be damaged, or the body may need to be replaced.
Or you may have a blocked barrel, try cleaning it.