There are a few differences in the CZ safety and decocker models. The differences that pertain to this modification or fix are the design of the sear cage pin and how the sear cage is retained in the pistol frame.
In a CZ75 variant model decocker the sear cage pin not only retains the sear cage parts in the sear cage but also retains the sear cage in the pistol frame. A CZ decockers sear cage pin is longer than that of a safety models. It goes through the sear cage and both sides of the pistols frame. This design has the benefit of maintaining the sear cages position in the frame more solidly and allows for less sear cage movement while the trigger is pulled.
Edit: Clarification: In aluminum framed CZ 75 variant pistols the sear cage pin may only go through the right side of the frame. The left side of the sear cage pin may be stopped by a fixing insert. I am unclear what bearing the difference in design has on sear cage stability at this time.
In a CZ75 variant safety model the sear cage pin only retains the sear cage parts. It is shorter than a CZ decockers sear cage pin and dose not go through the pistol frame. The sear cage in a CZ safety model is retained by the safety lever shaft. This set up offers the sear cage less stability and allows for movement of the sear cage within the frame in some instances. This movement can affect the trigger pull negatively which is more noticeable in single action. This can be more pronounced in a tuned configuration leading to a single action trigger pull that is less crisp than it would be otherwise.
One way to detect sear cage movement in a safety model CZ is to watch the safety levers while pulling the trigger in DA and SA. Because the sear cage is retained by the safety lever shaft, if the sear cage is moving the safety levers will also move or dance when the trigger is pulled. The severity of the sear cage movement differs from pistol to pistol, each factory CZ is a little different and some do not seam to move at all or not enough to be detectable. Some shooters will not be bothered by the sear cage movements effect on the trigger pull.
So if it ain't broke don't fix it. Shimming the sear cage is one option for sear cage stabilization. It comes with the side effect of complicating disassembly. Another option is to make a replacement #19 Hammer Pin Retaining Pin and hand fit it to a CZ 75 variant safety model. This can reduce or completely remove the sear cage movement. I recently completed this modification with positive results. My experience with this modification is detailed below.
Links to the reference threads i used for this modification. I believe these are worth reading as well:Sear Cage Movementhttp://www.czfirearms.us/index.php?topic=52047.0;topicseen
Another way to tighten a loose sear cagehttp://www.czfirearms.us/index.php?topic=63281.msg421884#msg421884 First i acquired material to fabricate a replacement #19 Hammer pin retaining pin. It is suggested in one of the reference threads to use 0.086 drill rod. The closest drill rod that i could find was 0.095. I cut an extra long peace so that i could chuck it in a drill and turn it down with sand paper to the desired diameter. You have some options on the final pin diameter depending on how you intend on fitting the new part. I ended up with a diameter a little over (0.086). After final fitting this still allowed for a looses enough fit so that the new pin could lean back a bit and contact/stop on the inside of the frame with the installed sear cage pushing on it. It seams that another option is to match the diameter of the new pin tightly to the hole so that the pin dose not rest on the frame. This may alleviate the pin interacting with the spring for the lefts side safety detent. I ended up removing a bit of material from the back side of the pin instead to allow for the spring clearance. In my case this worked out well, every CZ will be a little different. During fitting things should become more clear for the CZ that you are working with.
A reference picture of the #19 Factory hammer pin retaining pin.
A view of the #19 pin from inside the frame with the sear cage removed.
Factory #19 pin next to the replacement stating material
A reference picture of the pin installed after it was turned down but before it was cut to size. Once cut down to the correct size the replacement pin should not be higher than the rear of the frame next to the hammer. Once reinstalled the sear cage will cover part of the pin at the frame hole.
Alternative view from outside the frame of the pin installed after it was turned down to the correct diameter but before it was cut to size
Replacement pin turned down to size, cut to length, and
roughly notched out to make room for the sear cage.
Note: Once installed the sear cage blocks half of the hole for the factory #19 pin so the replacement pin being longer must be notched out to make space for the sear cage to fit into its orignal position in the frame.
Alternate view.
The final shape in my case was this.
Note: The notch in the pin starts at the top of the pin and runs down as far as the hole in the pistol frame. If the notch dose not run down far enough it may push the sear cage up once it is reinstalled, in my case this was not necessary. Each pistol frame and sear cage are a little different, observe and fit accordingly. Make sure to check the clearance of the top of the sear cage to the underside of the slide. If there is contact the top of the sear cage can be filed to fit.
Replacement pin cut down to size, it is now flush with the top of the frame next to the pistols hammer. This is the replacement pins final profile and length in my case. Each pistol is a little different the replacement pin must be hand to fit the pistol it will be installed into.
Final reassembly. Sear cage, Safety detents and Safety levers reinstalled. While test fitting the replacement pin it is a good idea to keep an eye on the safety detents, if they move they can impede the sear cages installation and it can feel like the replacement pin is causing the issue when it is not.
Make sure to check the pistols slide clearance to the top of the sear cage as well. Improper clearance can cause malfunction and or damage. Testing the fitment in my case required installing/removing the sear cage with and without the new pin in place to check the sear cages position. First without the safety detents installed then with the safety detents installed. Closely inspecting the rear of the sear cage that contacts the new pin helped with sizing and finding the correct angle.
Side view view of final reassembly. Cold blueing the replacement pin to color match the orignal is an option.
In the end this modification removed the final bit of creep/squishyness from the SA trigger pull of my DIY Pro Package CZ75 SP-01. The sear cage is now rock solid in the frame and i am pleased with the results. Doing this work took less time than i had anticipated and in some small ways gave me a greater understanding of the platform. It also lowered the single action trigger pull by a small margin. I will likely repeat this mod on a few of my other CZ safety models to test the gains.
Note: This post has been updated with input from forum members posts below.
