CZ 9mm 75B rear Comp Sight problem

[1SOW]

Angus, I've never posted you before, but I need some help.

About two years ago, I bought and put on the FO front and Comp Rear sights.   Less than a year ago the rear Comp sight broke off just behind the dovetail while shooting.

Rob said the Comp rear sometimes needed machining to clear the top of the slide.  He also sent me a new rear sight free of charge. I lightly sanded the top of the slide so a piece of thin paper would easily move between the sight and the slide.

TODAY that rear sight broke again while shooting ( I reload and shoot, USPSA production,  and steel Challenge using the same  125gr Zero jhp/n320, 130PF ammo).
The sight broke about 1/32" behind the dovetail.  Before it fell off, I was shooting way high at 10 yds, probably as it bent upward.   Looking at the dovetail portion of the sight(still in the slide), the top of it is well clear of contacting  the slide.

I need to know either what I'm doing wrong or what I should do/look out for so this won't happen again.

The last sight went in tight but smoothly using a leather lined vise and brass punch--no real hard punch hits needed.  I used a sight pusher to adjust for POI.

Does the dovetail on the sight need to be lightly polished with 1000 grit?

I know you can't see the break, but any advice you can give before I do this again is GREATLY APPRECIATED!!

Don Jones

[1SOW]

Anyone else have this happen?

[Cheesewhiz]

Anyone else have this happen?

I saw your original post a few days ago and I just couldn't see how this could happen. The gap between the slide and the comp. sight that I have on one of my SP-01's is about a matchbook cover thick and the hammer clears by about the same. I have run thousands upon thousands of rounds through that gun without issue. Is there anyway that the hammer clearance could be different on an 85?

....but that doesn't make sense either, you would see some sort of cycle upset, I would think, if there was contact.

Is there anyway it's an associated equipment contact issue, holster, shooting bench, truck, etc, etc?

Other then that I'm at a loss, sorry, I wish you well.

[1SOW]

Cheesewhiz:  It's not the hammer.  My 75B has the stock hammer that fully clears the sight.  

Since I replaced this sight I've reloaded and shot maybe 4000 rds as a guess.  
The first sight , as CZ Custom said, didn't quite clear the slide.  It had two small rub marks on the bottom side of the rear comp sight (that broke off); SOoo what they said made sense.  When I replaced this one, I lightly sanded the ribbed area under the rear of the sight until it completely cleared.  5-6 months later it broke in exactly the same place as the first one did.  This one bounced off my cheek and I never found it.

One thing I did notice before it separated, I was shooting way high.  I couldn't hit a popper at 10 yards- for 3 or four shots I was shooting just above it.  That means the sight was bending UP before it snapped off.

When I replaced the first one, there was at least one other poster who had the same thing happen.

I've also emailed CZ CUstom shop about this on 2 Dec., and haven't had a reply yet.

I can borrow my son's Shadow ( ) , but I'm getting a little frustrated with this.   I don't want to repeat this again--maybe it's something I'm doing, but I don't think so.  

 

[Cheesewhiz]

What's the # rating on your recoil spring?

[eric0424]

It's possible your recoil spring is weak and the shock from the slide to frame impact is being transferred to the sight.  I believe you were hitting high just before it came off was because it was already cracked and bent upward.  Of course the only way to test this theory is to get another rear sight and a new recoil spring then see if or when it breaks again.

[1SOW]

Cheesewhiz:  I'm running an 11# recoil spring and never shoot anything but my light 130PF reloads.

eric:  That's a thought

An 11# recoil spring (& 13# hammer) with USPSA Production class light loads is the "common" set-up for a CZ 75.  The lighter recoil spring is necessary for reliable extraction/ejection.

You guys might be on the right track though,  my recoil spring was a pound or two heavier with the first Comp Rear sight.  It lasted  about twice as long as this last one.  Who knows?


I found this on the Custom site:  * A sheet of computer paper slid loosely under the site after my  install.

CZ Custom Competition Rear Sight
CZ 75 85 97B all Standard Dovetail Cuts
Will require 6.5mm Front Sight.

May require some minor fitting, please check there is a  light gap under the sight blade after fitting.
If the rib is touching the underside of the sight it can put pressure on the sight blade and cause breakage.

[eric0424]

Does the sheet of paper go all the way to the sight base??  The gap should be enough if it does clear all the way, a piece of the printer paper I have is .004" and if it fits loosely you probably have closer to .005.

Another option might be to use the recoil buffer for the CZ's, it may have to be fitted a little to keep the slide stop operational though.

[1SOW]

eric:  Yes, the paper went all the way to the dovetail and was loose--plenty loose.  I sanded & polished before I installed the sight. It was also easy to see light all the way to the dovetail.

[eric0424]

I think I would give the recoil spring and/or the buffer a try, it sounds like you've got plenty of clearance between the sight and slide.  Slide to frame impact is pretty violent and even more so if the recoil spring is too light or gets too old.  You would think with the low pressure loads you're shooting it wouldn't cause that kind of damage though.

[1SOW]

That's just the point:  I don't think the recoil impact of the slide to the stop is causing the problem.  My spring was almost new and many 75B competitors use this spring and sight package.  The slide does not 'slam' to the rear.

On the other hand, if I'm so smart why did the sight break?

I hope I hear from the Custom Shop---I'll call again tomorrow.

Oh, and the bad news:  they are "out of stock" on the rear sight.  S&!#!

Update:  I called and talked to Zoe today.  She said to send in my broken sight and she'd send me a new one--they are 'in' stock.
I removed the broken dovetail and went to the P.O. and sent it.  When I got back I had an email from Zoe saying my new sight shipped. Hooorahhh.

I still don't know what to do differently from the last time though.

[1SOW]

  I rcvd my new sight today and will probably install it tomorrow.

I'm  ready to consider any advice on the install.  I'm considering a light touch with 1000 grit on the sight's dovetail, so it won't take too much 'hit' to drive it in.  It has the setscrew to help hold it in position

Stuart?

rf?

Anyone?

[eric0424]

I honestly couldn't say, I  would be looking into a new recoil spring or the recoil buffer if it were mine.  Or maybe even a fixed rear sight, although you really should be able to use the adjustable sight without the breakage.

The only sight trouble I've had was on my TZ75, but it was the front sight, it wasn't breaking and I knew why it would fly off.  I didn't have the proper tool for the dual crimp posts, I finally used some solder and a center punch to keep it in place. 

[Stuart]

man...I wish I could tell you..I have not had one break..so I am not sure where the stress is coming from. it could be the sight cut is off slightly. not really sure where to go with this.

[1SOW]

Thanks anyway Stuart.  Maybe 3X is a charm.