This kit is recomended for best results and includes:

The SierraPapa Hammer. Manufactured in the USA from a solid block of high grade stainless steel. After machining the hammer is polished and hardened for long life and smooth operation, and finally the sear notch is hand-polished in our own shop to provide the smoothest possible trigger release.

The hammer is engraved "SP USA" to demonstrate BATFE Part 922R compliance.

The SierraPapa trigger. Manufactured in the USA from 6061 grade aluminum. After machining, the trigger is anodized to provide a durable, non-reflective finish. 

This replacement trigger is stronger and less flexible than the original CX4 plastic trigger, and features an adjustment screw that removes much of the objectionable pre-travel found in the original trigger group. The new trigger also features a permanently installed pivot pin for attachment of the first trigger operating bar. This ensures less flex in the trigger movement. Additionally, the slightly larger diameter of this fixed pivot pin removes some of the slack in the trigger movement. The result of this upgrade is a 6-6.5 pound trigger.

The trigger is engraved "SP USA"

SierraPapa reduced power hammer springs are manufactured in the USA from high grade spring steel. The new hammer springs are offered in two weights: light and medium. The light-weight spring provides the lowest trigger pull weight and it has been tested with complete reliability, using standard ammunition, in our test rifles. Theoretically there exists ammunition with "harder" primers. Our medium-weight trigger is an option for those who value ignition reliability with all possible ammunition types or who simply prefer a more positive trigger action in a combat carbine.

The reduced power hammer springs. Installing the reduced power hammer springs with the original CX4 plastic hammer may result in unreliable firing pin operation. The lighter weight of this spring causes it to be relatively more susceptible to the influence of each part of your CX4 when measuring trigger pull weight.