If we install the hammer/trigger/spring upgrade parts into your trigger housing (or even if you do it yourself) it may be necessary to repeat the adjustment of the trigger adjusting screw after your CX4 has been in use for a short time. Because of the way they are made all CX4 trigger housings vary a little in size, we adjust the trigger in one of our test guns so your gun may be slightly different and the screw may need to be adjusted to match your gun. This is a simple adjustment but go slowly, adjusting the trigger adjustment screw a little at a time, until you find the correct position. The good news is that once the adjustment is made correctly it should not need to be repeated for many rounds fired.
First, the symptoms. The most likely symptom of incorrect trigger screw adjustment will be that the gun fires correctly for the first round after chambering a round using the cocking lever but it subsequently fails to fire in semi-auto. The trigger will be free to move through it's full range of travel but there is no hammer release. If the case is a slight mis-adjustment the failure to fire may be quite infrequent but the feeling will be the same, full and free trigger movement but no hammer release. In a mild case it may be that a pushing the trigger forward will allow the gun to be fired after an initial failure.
IF THIS TYPE OF FTF HAPPENS BE CAREFUL. THERE IS NOW A LIVE ROUND IN THE CHAMBER AND THE GUN MUST BE UNLOADED AND MADE SAFE BEFORE YOU DO ANYTHING ELSE.
Solution.
Find the special Allen wrench we supplied, it will probably be in the small plastic bag containing your original parts. Remove the upper of the gun from the lower. Find the adjustment screw (see photo in post below). Engage the wrench into the screw (I know, this is fiddly but this is the only place we could put the screw). UNSCREW the screw about 1/8th. of a turn (because of the tight space this is about the maximum you will be able to unscrew the screw in any case). Assemble the gun and perform a live fire test on the range since a dry fire test does not give accurate results.
Results.
If, after you have made the adjustment, your gun works properly the problem is solved. If the problem is not solved try another small adjustment. If the problem is still not solved then please 'phone us since there may be other factors involved. The adjustment is pretty critical. If the screw is screwed too far in then the trigger will not reset and the gun will not fire. If the screw is adjusted too far out then the gun may be difficult to cock (after adjustment you should still be able to cock the hammer with your thumb with the upper removed).
Back story.
As with all semi-automatic firearms there must be a way to disconnect the trigger of the CX4 from the rest of the firing mechanism to prevent the gun going fully auto. You probably would not be surprised that this mechanism is called - the "disconnector". This is how the disconnector works on the CX4.
If you look underneath the trigger housing you will see that the rear end of the forward trigger bar (the one with the 90 degree bends around the magazine in it) has a hook on it. This hook connects with a projection on the forward end of what I call the rear trigger bar. With the gun in a ready to fire state the hook and projection are engaged with each other. As you pull the trigger the forward trigger bar pulls the rear trigger bar (and the hammer pivot pin) forward. The hammer pivot pin, of course, pulls the hammer forward and the hammer disengages from the sear allowing the hammer to rotate upwards and strike the firing pin. After the cartridge ignites the bolt is pushed rearward. Up until this point a projection on the top edge of the forward trigger bar had been resting in a cutaway on the lower right-hand surface of the bolt. As the bolt moves to the rear the projection on the forward trigger bar is forced down by the bolt which forces the hook at the end of the forward trigger bar to disconnect from the projection on the forward end of the rear trigger bar and the trigger is DISCONNECTED from the hammer mechanism. Eventually the bolt returns to the forward position loading a new cartridge and allowing the projection on the top of the forward trigger bar to enter the cutaway in the bottom of the bolt, then, when you allow the trigger to go forward again the hook and the projection reconnect and you are ready for the next shot.
Quite simply, what is happening when the trigger adjusting screw is too tight is that the hook on the forward trigger bar is not reconnecting with the projection on the rear trigger bar. Unscrewing the screw a little allows for correct re-engagement.