How the M3 works
Also how most blowbacks work.
Here's what should happen when you pull the trigger:
* Pull trigger
* Solenoid pushes the sear
* Sear releases the hammer
* Hammer travels forward from the spring pressure
* Bolt is linked to the hammer so it also travels forward to load a ball into the barrel
* Hammer hits the valve
* Valve opens firing the paintball and also blowing the hammer back (blowback)
* Bolt is linked to the hammer so it also travels backwards
* Spring pushes the hammer forward BUT
* The sear catchs the hammer to keep it from firing again
This general understanding should help you troubleshoot any problems you may have.