Basic Installation.

Fitting of the SierraPapa stainless steel hammer is very simple. It is a drop-in replacement for the original CX4 hammer and no gunsmithing work is routinely required. However, if you are not totally comfortable with performing the fitting operation yourself we recommend that you delegate the work to a qualified gunsmith. To ensure the best possible performance from your new hammer we suggest that you examine some other parts of the hammer mechanism for problems while you have the trigger group disassembled. These checks are covered in a later paragraph.

As you replace your CX4 hammer you will probably also replace the original hammer spring with a SierraPapa reduced power item. This is simply a matter of swapping the springs.

To carry out the basic disassembly of the trigger group and to fit your new hammer please refer to the excellent instructions provided by Tactical Excellence. This information can be found here.

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A hint that may help in re-assembling the CX4 hammer group.

Make yourself a small alignment pin as shown in the bottom of the photo. This is a length of steel rod 3/4 of an inch long that is a good sliding fit in the hammer pivot pin hole (about 5/32 of an inch). I actually made my pin from a convenient nail. File and polish a point on the alignment pin as shown. Since the pin does not receive hard use any soft metal is OK. The only criteria are that the pin should be a fairly close fit in the hammer pin hole and the finished pin must not project out of the ends of the hammer pin hole when the hammer group is assembled.

Use is simple. Assemble the hammer group on the alignment pin then put the hammer group into the trigger group housing. Line up the various pivot pin holes and push the alignment pin out (from the flat end) with the actual hammer pivot pin. The alignment pin holds the rear trigger bar in position during assembly and the point on the alignment pin lines up the holes at the "exit" end of the trigger group housing.

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Checking the Trigger Bars for Burrs and Bends

The two flat metal trigger connector bars fitted to the CX4 are punched from a sheet of metal. This punching process can sometimes leave burrs or rough edges on the parts that will cause roughness in the movement of the trigger mechanism. The burrs generally occur on the right-hand side of the trigger bars (as viewed from the stock end). While you have the trigger mechanism apart check the surfaces of the trigger bars that slide inside the slot in the hammer to detect burrs and remove these burrs with a fine diamond file. Burrs often occur around the pivot pin hole in the rear trigger bar.

The forward trigger bar is bent to follow a path around the magazine housing. We have found that in some rare instances the bends are not accurately made resulting in binding between the hooked end of the forward trigger bar and the slot in the hammer itself.

Above. Side view of the front trigger bar.

Above. Top view of the front trigger bar.

This is the area of the trigger bar that can cause problems.

The end of trigger bar must fit into the slot in the hammer without excessive binding.

After assembling the trigger mechanism you will, of course, try your CX4 at the range. If all functions and adjustments are normal - enjoy.

Should you experience problems such as the inabilty to adjust the trigger pull accurately or infrequent misfires I suggest that you dissassemble the trigger mechanism and then make a trial installation of the hammer and trigger into the trigger housing without fitting the hammer spring or the rear trigger bar. When the test assembly is complete move the rear end of the forward trigger bar manually in the hammer slot to check that no undue binding occurs in the movement. Light rubbing contact is normal but if there is a distinct binding of the trigger bar in the hammer slot adjustment may be required. Please contact us at 503-621-3017 to report any problems and we will advise on corrective action.

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Lubrication

During and after installation please lubricate the hammer assembly of your CX4 in the same way as you would lubricate the hammer of any other firearm that uses steel components. One additional lubrication action we recommend is the application of a film of good gun-grease on the surface of the hammer that slides past the fixed plastic sear during the cocking sequence.

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To be continued