M4 GBB WE burst randomly on semi.
 

Well so I bought this WE replica from a dude.

I opened it,painted it and cleaned it.

The only problem it has is that sometimes on semi it burst randomly then goes back to normal semi.

I removed the auto sear as it doesnt seem to change anything.

I dont know which gen it is as there is no engraving or anything.

Is it open bolt?

First thing to check is the o-ring on the gas piston. Remove the BCG, pull the piston forward and oil the o-ring at the back with pure silicone oil.

Also what kind of gas are you using? Is the bolt cycling all the way back? A weak (partial) cycle can give you a sloppy sort of burst. Do you have an NPAS installed?

Open bolt yeah.


Propane

Try replacing the Sears.
Kyairsoft has the part.
A few bucks plus shipping

Replacing the Sears can be done by following some videos online