Custom RMR/SRO adapter plate for CZ-75 (SP-01) Project

[earlan357]

I want to setup my SP-01 Tactical with the new Trijicon SRO for competition but before I send it off to an established company, I want to see if anyone will accept a custom job.  I haven't found a place that install an RMR adapter plate much lower than the top of the slide and the CZC RDS plate leave some pretty large gaps.  I get that they're trying to avoid the FP retaining pin and FP Block recess but I'm thinking this can work if I start with a steel plate.  It should be strong enough to support the FP block and retainer since the forces aren't really that great, and the sheer forces are contained by the pocket walls, while the 1911 adapter style saddle prevents the pin from sliding out.  I figure offsetting the mounting screws will better distribute the forces and with the deeper cut, it can be mounted farther back to clear the extractor pin hole.  With the top of the plate surface .125" below the top of the slide, the optic body will be supported by the pocket instead of relying on the two round lugs.

Before you ask if .125" is really worth it, I'm one of those people who hates to leave anything on the table.  Having the window low means my peripheral vision can pickup the top of the slide or front sight sooner as I press out from the draw and guide the dot to my eyes.   I have no problem chasing grams, or thousandths of an inch.  Even if the performance benefit is minimal, just knowing it isn't as close to perfect as it can be will haunt me to my grave.  As an added bonus, at that depth I can run a .315-.330" tall front sight.  By milling a channel at the rear of the optic body and color filling it white, I can "dot the i" with the fiber dot and get a rough iron sight picture on the off chance my optic dies mid stage.

I work in the racing industry and have access to a 2-axis CNC mill at our shop.  I've been playing with it, doing minor projects after hours but I'm no machinist.  I even have the CNC program written out and ready to test in delrin, but steel is a completely different thing and I know that there's a lot I don't know.  Since I don't have a spare 75 slide to test on, I'd rather pay a professional since spare slides aren't exactly cheap or plentiful.  So does anyone know of any shops that might be willing to take on a project like this?

[Tok36]

As an example of how low you can go, CZ Customs did this one.

[M1A4ME]

Not sure of the reasons for "fear" of the firing pin block spring.  Maybe it's not so much the spring as the travel distance required.

If I remember correctly my M&P's striker block spring pops out the top of the slide when replacing the rear sight.

Again, it may be a travel distance required to work properly thing, not an issue with the spring.

[earlan357]

So I mocked up a "slide" with some aluminum to test my CNC programming and roughed in the pocket.  Fits nice and tight.  Mounting screw holes and countersinking is next  The plate was a free UTG RMR mount that I hacked into a plate.  Measuring my slide, I can get away with a .240" deep pocket without intrusion into the FP retainer pin hole.  A .060" deep pocket in the plate will make room for the FP block.  With a .125" thick plate, that'll mount my optic just .010" higher than on my Glocks.  I should be able to position it just far back enough to clear the extractor pin, and it's deep enough to get good rear support from the slide.  I'm debating staggering two 6-32 screws to secure the mount, or squeezing in four.  Does anyone know the steel  composition of modern CZ slides?  I'm currently figuring RPM and feed rates for 4140 steel hardened to 30RC.

[earlan357]

Update:

After a lot of measuring and thought, I picked up a Trijicon RM-62 Steel RMR Block to start my custom RMR mount project.  At .360" thick I needed to thin it down.  My goal was between .100" and .110".  This would leave enough thickness for the RMR screws to get 3 full turns of engagement and enough room to countersink the mounting screws.  The first problem was figuring out a way to hold it in the mill.  I grabbed some scrap aluminum, and made a jig that holds the mount upside-down in the vise.  It uses the recoil bosses and pocket to keep the mount in place, while 6-32 screws thread in from underneath to hold it down.  The large hole in the middle was so I could push the mount out due to the tight fit in the pocket.

Freshly machined jig.


Perfect fit.


Secured from underneath with 6-32 screws.


After face milling and sanding.


0.1055" thick.


The next step is to mill my SP-01 slide to accept the mount and drill, tap, and countersink the mounting holes.  After that, it's gonna get sent off to CGW to have the front serrations extended, and to have the slide and mounting plate Cerakoted.

[earlan357]

I finally bit the bullet and started cutting on my slide.  After more careful measuring, I settled on a pocket depth of .230" with a .110" thick plate.  This buries the optic .120" deep.  While I could have just deleted the firing pin block, I needed to keep it to stay Carry Optics legal.  So I bored out a hole in the adapter plate.  The RMR sealing plate takes over as the roof of the FP block hole.  This reduced the depth of the hole by .030".  I had to clip 3 coils off the FP block spring, but it fully deactivates with no binding.  I settled on 4 x M3 screws for the mount.  That's twice as many as CZ uses on their optic ready slides, and they offered the right balance of strength and size.

Slide cut.


Adapter plate fitted.










Now it's off to CGW to extend the front cocking serrations and matte black Cerakote.  I'm debating having the adapter plate Cerakoted to match the slide, or go with red to match the other accented parts.

[MoRivera]

Really nicely done.  Kudos for chronicling the process.

[Earl Keese]

Well thought out and nicely executed like your other projects. Thanks for sharing. Was the decision to build a tactical instead of a Shadow driven by a preference for the de-cocker?

[Sulpgnir]

Now that's precision work!  Thanks for sharing.

[Genin]

Wow, that is some nice work. It was very well thought out and executed. I love when people do their own improvements and they come out nice like that. Bravo.

[earlan357]

Well thought out and nicely executed like your other projects. Thanks for sharing. Was the decision to build a tactical instead of a Shadow driven by a preference for the de-cocker?

Sort of.  The Tactical was a range rental they were selling for $350.  But I like the de-cocker because the rearward lever position lets me get a higher support hand grip on the gun than the safety, and it lets me start stages with the DA trigger pull from half-cock.  I figured It was cheap enough that I could risk messing with the slide.  The SA trigger isn't as good as a Shadow due to the FP block(longer reset too) , but coming from a striker-fired guns, it's still fantastic after adding the CGW pro kit.   Plus I won't need to mill out the slide to make Carry Optics weight.

[Earl Keese]

Well thought out and nicely executed like your other projects. Thanks for sharing. Was the decision to build a tactical instead of a Shadow driven by a preference for the de-cocker?

Sort of.  The Tactical was a range rental they were selling for $350.  But I like the de-cocker because the rearward lever position lets me get a higher support hand grip on the gun than the safety, and it lets me start stages with the DA trigger pull from half-cock.  I figured It was cheap enough that I could risk messing with the slide.  The SA trigger isn't as good as a Shadow due to the FP block(longer reset too) , but coming from a striker-fired guns, it's still fantastic after adding the CGW pro kit.   Plus I won't need to mill out the slide to make Carry Optics weight.

$350 was a steal! Thanks for clarifying.

Sent from my XT1254 using Tapatalk

[recoilguy]

That is some real nice work.
I like to see this kind of thing happening.
Nicely played sir!!!

RCG

[mushkin]

Fantastic work.

Could you please provide measurements for the location of m3 screws? How deep did you drill and thread into the slide?

Thanks 👍🏻👍🏻

I want to setup my SP-01 Tactical with the new Trijicon SRO for competition but before I send it off to an established company, I want to see if anyone will accept a custom job.  I haven't found a place that install an RMR adapter plate much lower than the top of the slide and the CZC RDS plate leave some pretty large gaps.  I get that they're trying to avoid the FP retaining pin and FP Block recess but I'm thinking this can work if I start with a steel plate.  It should be strong enough to support the FP block and retainer since the forces aren't really that great, and the sheer forces are contained by the pocket walls, while the 1911 adapter style saddle prevents the pin from sliding out.  I figure offsetting the mounting screws will better distribute the forces and with the deeper cut, it can be mounted farther back to clear the extractor pin hole.  With the top of the plate surface .125" below the top of the slide, the optic body will be supported by the pocket instead of relying on the two round lugs.

Before you ask if .125" is really worth it, I'm one of those people who hates to leave anything on the table.  Having the window low means my peripheral vision can pickup the top of the slide or front sight sooner as I press out from the draw and guide the dot to my eyes.   I have no problem chasing grams, or thousandths of an inch.  Even if the performance benefit is minimal, just knowing it isn't as close to perfect as it can be will haunt me to my grave.  As an added bonus, at that depth I can run a .315-.330" tall front sight.  By milling a channel at the rear of the optic body and color filling it white, I can "dot the i" with the fiber dot and get a rough iron sight picture on the off chance my optic dies mid stage.

I work in the racing industry and have access to a 2-axis CNC mill at our shop.  I've been playing with it, doing minor projects after hours but I'm no machinist.  I even have the CNC program written out and ready to test in delrin, but steel is a completely different thing and I know that there's a lot I don't know.  Since I don't have a spare 75 slide to test on, I'd rather pay a professional since spare slides aren't exactly cheap or plentiful.  So does anyone know of any shops that might be willing to take on a project like this?