The following are a few comments which should allow us to make life easier for you during these kit installations. Some comments will cover the actual hardware installation and some are explanations of how the CX4 works which may help you to troubleshoot problems,
So, here goes, in no special order.
Parts for Trigger Upgrade.
If you send a trigger assembly to us for upgrade include the following parts.
a. The trigger housing including the original trigger and hammer components.
b. The bolt stop lever, part number 39 in the Beretta parts diagram for the CX4.
Link : https://www.brownells.com/schematics/Beretta-/CX4-sid873.aspx
(This is the original Brownells parts diagram, thanks to Brownells.)
The reason I would like to have the bolt stop is because it can be very fiddly to reinstall the bolt stop without accidentally distorting the trigger spring (part 35, which can cause all sorts of problems). Send the bolt stop and I will re-install it for you. (See comment under "Safety Button" below).
We do not need the safety button or the bolt stop release lever.
As you have probably worked out by now the trigger housing is secured into the CX4 lower by the safety button. To stop the safety button falling out during normal use this part is held in place by a triangular projection on the lower edge of the bolt stop lever. To remove the safety button you need to lift the bolt stop lever just enough for the safety button to be pushed free (this can be done in either direction). YOU DO NOT NEED TO REMOVE THE BOLT STOP LEVER COMPLETELY FROM THE TRIGGER HOUSING IN ORDER TO REMOVE THE SAFETY BUTTON. Simply lift the bolt stop lever sufficiently to allow the safety button to be pushed out of the lower and the trigger housing.
Of course, to lift up the bolt stop lever you will need to free its rear end from the bolt stop release lever first. This operation is covered in our trigger housing disassembly video.
Now, when you replace the safety button into your upgraded trigger assembly MAKE SURE IT IS ORIENTED CORRECTLY. I have had more than one phone call telling me that the gun would not fire because the trigger could not be pulled. It usually does not take much time to find out why. Remember, the safety button can be reversed for right or left hand shooters but it can also be fitted upside down!