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Help me troubleshooting this gun

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I own a King Arms M4 (V2 gearbox) that shoots perfectly until now.


Unfortunately it seems like the shell was cracked, so I had to replace that one.


This is what I've done:

- Replaced the shell ( A used G&P shell)

- Upgraded the Cylinder to a 4/5 (I'm using a Ver. 2 Black Python 363mm Tight Bore Barrel)

- Upgraded the Cylinder head (ASG Lonex I think)

- Shimmed the gun


Since I had to skirm the day after I didn't had a lot time.

While reinstalling the upper receiver I couldn't close it properly because the nozzle didn't lined up perfectly with the hopup.

Again, I didn't had much time so I just took the hopup and fitted the nozzle manually inside it. After that I could close the gun.


The day after, I did my fps test and had about 350 fps. Perfectly. Most bb's flew good but sometimes there was one bb that didn't went as far as the others.

The gearbox sounded like it wasn't shimmed perfectly.


So after that day I opened my gearbox and reshimmed it perfectly. I also found out that I still had a nice piston so I upgraded it with a Madbull Airsoft PX-02 Piston Body With Full Metal Teeth. After reassembling the gun I realy had a hard time to slide the upper receiver on the lower; I had to push pretty hard to get it fit.


When testing it seemed like the BB's were not chambering, the alluminium nozzle (that worked for years) seemed to be a tiny bit too far in the hopup that caused the bb's not going in.

Now the weird part.

If I assemble the gun and I attach the grip first, it seems like the hole from the rear receiver pin isn't alligned with the gearbox anymore. The upper receiver slides perfectly in the hopup, and It chambers perfectly.



Sorry for my bad english. I realy hope u guys can help me on.






Edited by Awaces

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