CZ 455 Bolt flies out - Resolved

[PaperPuncher]

About 10 times in maybe 1-2000 rounds, the bolt in my newish CZ 455 keeps going when I pull it back to cycle the next round. Sometimes I have caught it, sometimes it has hit the ground. I am not holding the trigger back.

I just cleaned everything that didn't require special tools or removing pins and couldn't find an obvious reason. Called CZ and was told they have not heard of that problem with the 455. On the 452/453 it was known to happen rarely with the trigger tension backed all the way off.

With that in mind, here's my diagnosis: The trigger spring tension nut clicks every quarter-turn (it's square). When it is backed all the way off, it no longer clicks and can turn freely. If it's not square in the slot in the stock, it can contact both sides of the slot at once. MAYBE that can cause enough drag to prevent the trigger from resetting immediately. MAYBE that can release the bolt.

So I tightened up the nut just enough to click and stay in place. That did not change the trigger pull enough to matter. I'll post again when I decide whether it fixed the problem but that could take a month or more. In the meantime, if someone can add to this - please do.

[PaperPuncher]

Update: It still comes out. Did it again today. So putting a small amount of tension on the trigger spring adjustment nut didn't change it.

I load each shot deliberately. Bolt up, bolt back, stop and check to see that the case really ejected and the next cartridge is lined up, bolt forward, bolt down, fire, repeat. I flip it briskly but not violently back because I want to be sure the spent cartridge ejects cleanly. I don't really grip it but don't think I should have to (somebody please correct me if I'm wrong). One time today, the bolt just dropped back out of the barrel and was stopped by my hand.

The rifle was freshly cleaned, shooting beautifully. I shot 100-125 rounds (all target quality and subsonic - nothing overpowered) and it happened once. Any ideas?

[ZG47]

If you have eliminated spring tension issues, I suspect that you either have a radius where a flat edge is required or that something was milled/ground slightly further than factory spec.

Comparison of the critical parts on your rifle with those on an identical model is the obvious next step.  If you cannot do that, you need to visit a genuine gunsmith. Given that the Brno .22 rifles trace their ancestry back to pre-WWII military training rifles, I suspect that it would be a relatively simple task for a qualified professional to identify the cause of your intermittent problem and eliminate it.

[Plink]

Would factory warranty be an issue?  They might give you full replacement.   Contact them.

[PaperPuncher]

I had some suggestions on another forum and just spent a long time with dye, magnifiers, lights, etc. understanding what happens. The consensus seems to be that it's insufficient engagment between sear and bolt or too much drag between the trigger and sear as the trigger resets. The second of those could lead to the first.

I'm sure CZ would take care of this but I don't want to send it back if I can possibly avoid it.

Yes, I would like to compare parts with another one. I recently spent some very productive time interchanging 10/22 action parts from several rifles and manufacturers, but don't know where to find a 455 to compare. I'm not ready to pay a gunsmith.

I really like this gun and I don't like giving it bad press. It's a mighty fine rifle for less than $400. This might go away with time and maybe some polishing of parts that I'm not ready to remove yet but will someday.

[Nupes]

There are some good suggestions at Rimfire Centrals's site in the CZ section for this problem since it occaisionally comes up.  Consensus seems to be that its either dirt/debris  or shallow sear engagement.   If your trigger consistantly has little or no take up/creep then the second problem is most likely.  A bump test for safety sake sometimes validates insufficient sear engagement.  Also take a look at the sear engagement point and see if you notice one side worn shiney more than the other...this would indicate a misalignement issue between the surfaces; this too, will cause insufficient sear engagement.  Cause of this would be bent pins, machining errors on parts, or someone heavy handed on drifting out the pins.   Many people find that .007"-.013" engagement between the surfacesworks well for reducing creep to acceptable levels.  There is about a 3:1 ratio on this measured distance that shows up in trigger  take up.   Start going below this amount, and the rifles begin to fail the bump/safety test in my experience.

[buddy.223]

im sure youve checked the top of the sear hasnt broken off, ive heard it does happen.

[PaperPuncher]

I finally sent the rifle back for service under the warranty and now it's fine. Have run a couple hundred rounds through it since it came back. The bolt stays in and feels smooth and solid. The CZ-USA Warranty Log document enclosed with it said "Replaced sear due to a improper machined surface."

There is a short vertical lip on the back of the sear, opposite the one that engages the trigger, that keeps the bolt in. I can't measure it without taking the sear out, but it looks like about 1 mm or a little more than 1/32" deep. I don't remember such an obvious lip on the original sear.

They also replaced the walnut stock. I had mentioned some small dings in the top of the stock just behind the action from the bolt hitting it. I could have lived with the dings and didn't expect them to replace the stock. The new one is nicer than the old one.

No matter how fine these rifles are, they are relatively inexpensive and mistakes will get out the door. I have found, as have many other people, that some companies are very good about making it right and some are not. I have experienced both. I wish it had been right the first time, but appreciate that CZ-USA did what they could to make it right.

[ZG47]

Regardless of price, the law of averages will apply. Great to hear that it is sorted. Have fun.