CZ P-07; hammer falls to half cock instead of fully dropping?

[2A-Hoosier23]

I'm a rookie and may not use all the correct terms but any help here would be highly appreciated.

I have a 9mm CZ P-07 with the full Cajun Gun Werks Pro Upgrade kit, 1600 rounds thru the gun after the kit was installed by a local gunsmith. Last range trip 3 days ago I fired 270 rounds through the gun and had my first 2 malfunctions, both failures to fire, both seemingly light primer strikes (dimpled primer) with S&B 115 gr FMJ, maybe 3-4 magazines in between the failures. Both rounds were re-chambered and fired, the first took 3 more trigger presses/hammer strikes before going off, the second took just one more.

Just now in dry fire practice i noticed something I hadn't before. When pressing the trigger very slowly I got the hammer to fall to the half cock position, then after added pressure on the trigger, it fell from half cock to full drop. I was able to do this a couple more times, deliberately pressing the trigger very slowly and watching the hammer. I couldn't recreate this from single action dry fire, only from double action, but both of the live ammo failures that happened on the range were in single action, and I have no idea if the hammer was doing the same thing. The 2 malfunction bullet primers were clearly dimpled, though, so not sure if that would answer that.

other details that might matter:
The first ~1100 rounds through the gun were Speer Lawman 124 gr TMJ, along with some Federal 124 gr HST's, no failures
I dry fire regularly. draw from concealment, one shot on target (so most reps are double action) probably 200+ reps a week
I don't dry fire practice single action NEARLY as much as double action, maybe like 30:1 ratio
I use snap caps when dry firing

I tried to cover everything I could think of. Any input would be greatly appreciated!

 

[Hohn]

Decocking it's normal to have it drop to half cock for a P-07.

The hammer should never fall to half cock with the trigger. Under ANY condition.

I think your 'smith may have erred somewhere.

 

[churchmouse]

Decocking it's normal to have it drop to half cock for a P-07.

The hammer should never fall to half cock with the trigger. Under ANY condition.

I think your 'smith may have erred somewhere.

Yes something is amiss here.

There is a long running thread that is pretty much dedicated (most times) to all things CZ. With some off topic discussions like pantless endevers etc but some one in that thread will know why. Most likely Llh1956.

https://www.indianagunowners.com/forums/handguns/460777-czickness-xviii-prepare-winter.html

 

[88E30M50]

That’s a tough one. The light strikes could be coming from a dirty firing pin channel, but that doesn’t sound right to me. What color hammer spring are you running? IIRC, I’m running the yellow 18# spring in my P07s and have had the rare failure to fire on one of them. It’s my 9mm P07 that has had that, but I have not seen that with either of the .40 P07s.

I’d check to see if the roll pin was installed with the opening facing up. If not, maybe pull it to see if it’s deformed. It should not be since you’ve been diligent about using a snap cap, but that could cause light strikes. If you are running the gold 15# spring, step up to the 18#. I have had issues running the gold springs before with some primers.

The issue of the hammer falling to the half cock notch could be an incorrectly sized roller. The roller is how CZ tunes the timing of the P07/P09 series. They can be as small as .210 up to .230 from the factory. My 1st gen P07 in .40 came in with a .212 roller. The newest gen 2 .40 P07 was .224. It’s better to go bigger than smaller as issues can happen with an under sized roller. The standard Pro kit comes with a .225 roller, but you can order other sized in increments of .005.

If you have the original parts and a micrometer, check the diameter of the original roller. If it’s a ways off from .225, try swapping the original back in to see oil that makes a difference. I had to swap rollers around on my latest one to get it to run properly. The factory roller really does not make that big of a difference in how smooth the gun feels when done.

 

[2A-Hoosier23]

Decocking it's normal to have it drop to half cock for a P-07.

The hammer should never fall to half cock with the trigger. Under ANY condition.

I think your 'smith may have erred somewhere.

Right, I'm only talking about falling to half cock with the trigger, and that's what I thought. Thank you

 

[2A-Hoosier23]

.

 

[2A-Hoosier23]

Yes something is amiss here.

There is a long running thread that is pretty much dedicated (most times) to all things CZ. With some off topic discussions like pantless endevers etc but some one in that thread will know why. Most likely Llh1956.

https://www.indianagunowners.com/forums/handguns/460777-czickness-xviii-prepare-winter.html

Perfect, I'll head over there for future reference, ty

 

[2A-Hoosier23]

What color hammer spring are you running? IIRC, I’m running the yellow 18# spring in my P07s and have had the rare failure to fire on one of them.

I’d check to see if the roll pin was installed with the opening facing up. If not, maybe pull it to see if it’s deformed. It should not be since you’ve been diligent about using a snap cap, but that could cause light strikes. If you are running the gold 15# spring, step up to the 18#. I have had issues running the gold springs before with some primers.

The issue of the hammer falling to the half cock notch could be an incorrectly sized roller. The roller is how CZ tunes the timing of the P07/P09 series. They can be as small as .210 up to .230 from the factory. My 1st gen P07 in .40 came in with a .212 roller. The newest gen 2 .40 P07 was .224. It’s better to go bigger than smaller as issues can happen with an under sized roller. The standard Pro kit comes with a .225 roller, but you can order other sized in increments of .005.

If you have the original parts and a micrometer, check the diameter of the original roller. If it’s a ways off from .225, try swapping the original back in to see oil that makes a difference. I had to swap rollers around on my latest one to get it to run properly. The factory roller really does not make that big of a difference in how smooth the gun feels when done.

The gold 15# is currently installed so I'll move it up to the 18. I'll look into getting a micrometer since it seems handy for a lot of other things. Thank you very much

 

[gmcttr]

Also call CGW. They are extremely helpful.

 

[88E30M50]

The gold 15# is currently installed so I'll move it up to the 18. I'll look into getting a micrometer since it seems handy for a lot of other things. Thank you very much

I could not get reliable, consistent ignition with the 15# spring. I think that it’s meant for competition where you can reload a specific brand of primer that’s known to be soft (CCI maybe).

Moving up to the yellow should correct that component of the issues you’ve been having. The other issue might just be a case of the incorrect sized roller. If you have the factory parts from the gun, you can try to reinstall that roller to see if it makes a difference.

 

[2A-Hoosier23]

I could not get reliable, consistent ignition with the 15# spring. I think that it’s meant for competition where you can reload a specific brand of primer that’s known to be soft (CCI maybe).

Moving up to the yellow should correct that component of the issues you’ve been having. The other issue might just be a case of the incorrect sized roller. If you have the factory parts from the gun, you can try to reinstall that roller to see if it makes a difference.

Thanks, I'll first move up to the 18 spring before doing anything else like the roller, it makes sense in my mind to try to isolate the problem so change one thing at a time, right?
Also, what ammo were you using that was causing inconsistent ignition with the 15# spring?

 

[Sigblitz]

Just a thought, but too light of a hammer spring? Possibly causing a dead spot.

 

[2A-Hoosier23]

Just a thought, but too light of a hammer spring? Possibly causing a dead spot.

I believe that's what it turned out to be - switched to the 18 lb spring, sent 220 rds downrange so far with no issues, but it took well over a thousand rounds on the lighter 15 lb spring before i started having issues, so time will tell

 

[2A-Hoosier23]

Update... Today's practice marked 6000+ rounds ever since I ditched the 15lb hammer spring for the 18lb yellow hammer spring. Plenty of double-action dry-fire trigger presses too, which was where I first noticed the original problem.

Since the swap, not once has the hammer dropped to half-cock when it should drop fully. Not in live fire or in dry practice. If the trigger is pressed, the hammer hits the firing pin, as it should.

And since the swap, I have had a total of two light primer strikes in those 6k+ rounds, both with harder Wolf primers. One happened during a Steel Challenge match so I just pressed the trigger again and the second hammer strike ignited the round.
The other happened during a practice session so I had time to eject the round and verify the problem (dimpled primer), then I rechambered it and it fired on the next strike.
I think I can chalk that up to hard Wolf primers because it hasn't happened once with other brands such as CCI, Speer, Federal, PMC, Fiocchi, S&B, probably a few others. Only Wolf caused light primer strikes. And only two in probably 4000+ rounds of Wolf.

I never did check the roller size (per 88E30M50's suggestion) because the hammer spring swap fixed the issue. But I'm nearing the point where I'd like to fully disassemble the gun for a thorough cleaning and inspection so that will be a good time to do so, I will post an update when I get around to that.

A big THANK YOU to 88E30M50, Sigblitz, Hohn, gmcttr, and CM for your helpful replies!

 

[88E30M50]

Glad to hear that it’s been run hard and has done well for you.