Does the gun cycle with no mag, and then NOT cycle with the mag inserted? Or does it cycle and just not fire?
The lack of a port (you called it an air hole) in the cylinder would not cause a problem. It simply allows for higher FPS in shorter barreled guns due to the piston being able to move faster. Longer barrels require a non-ported cylinder to get proper air volume. (I also installed a full cylinder in my M4 for higher FPS in the way of more air volume).
Without a mag inserted, pull the trigger and feel if any air is coming out of the barrel when you fire. If not, you have a problem.
Are the bb's chambering properly? Without a mag inserted, tip the gun upside down and drop a BB into the feed chamber. Does it go all the way in?
When you fire, can you see the nozzle moving?
If you can feel air out the barrel when you fire, you might have a broken tappet plate which is not allowing the BB's to chamber (because the nozzle isn't moving and chambering the BB). You might also have a problem elsewhere that keeps the nozzle in the way, preventing BB's from fully chambering.
We need more info in order to help you, bud.
