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cz 75 jams on 1st round of slide lock reload


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Have a pretty new CZ 75 CTS and a new to me but well used SP01. Am new to both of them.

Am feeding them with 147 sns bullets at 1.135" oal.

If you have the slide open and no magazine in either gun, the slide will close with a moderately hard wap to the magazine opening. Since both guns act the same my assumption is that this is normal.

On the 75, about 3 times out of 10 the gun will jam on the first round of a slide lock reload. The top bullet will be wedged with the nose on the bottom of the ramp and the slide partially closed and in contact with the upper portion of the base of the shell. It is as if the slide started to close when the magazine was just a little bit below fully inserted, maybe the magazine was still on the way up or maybe it bounced as it was slammed in.

It happens with at least 4 of 10 magazines, mostly mec gar but also cz. I suspect it would happen with all mags if I experimented some more, found that it happened on at least 4 and not all the same age & etc so I figured it was probably not a magazine issue.

Besides the issue mentioned, the gun(s) have been 100% reliable with the 147's and a hodge lodge of other recipes I have tried in them. I have not seen the problem in the SP01 but that may be because I have worked a lot more with the 75.

Any ideas on a fix would be appreciated.

The 75 does have a stronger slide spring in it than is needed (original spring, works fine but brass at 130 pf stays pretty close) was thinking about swapping it out & seeing if that effected the problem, also wonder if a bit of careful filing of the slide stop is the answer, I have no issue with trying different mags or loads if it gets back to that. Last thing I can think of is that maybe I just need to smooth out my reloads, I think if I was firm but dead smooth then everything would work ok.

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Thanks folks.

Will look hard at ammo as a first thing and play with oal, easy to check this out but not the direction my little mind was pointed in, have not got my head wrapped around why an ammo problem would only show up on the first round of a slide lock reload, if oal or case length is the fix then maybe I will learn something.

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How many rounds are loading in the mag? My Czechmate big stick will do this when I force that 29th round in the mag. 28 runs 100%. 29 runs 20%

10 rounds in 17 round mags (IDPA & USPSA production limit).

I tried to get the problem to occur in my SP01 today (same mags & same ammo) and could not make it happen.

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It's the bullets. Get a box of factory FMJ ammo and try to duplicate the problem. Also, try to load a bit longer...I use essentially the same bullet in my Shadow and I load to 1.150

Do not want to spike the ball on the 3 yard line, but I ran 200 at 1.15 with zero issues so far. Thanks!

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  • 2 years later...
On 10/8/2015 at 9:50 AM, GrumpyOne said:

 Also, try to load a bit longer...I use essentially the same bullet in my Shadow and I load to 1.150

 

7 hours ago, bschulte said:

I am having this exact same problem on my CTS. Did you ever find a solution?

 

147 SNS truncated cone at 1.135 was what I was having the issues with. Went to 1.151 & have since run several thousand through 4 different CZ's with no worries, none of the guns have had their barrels reamed.

 

Have since switched from being a CZ nut to a being Tanfo nut, mostly, the Tanfo's like 147 RN at 1.15 and that seems fine with the CZ's also but I have not run lots of RN through the CZ's so I would not spike the ball on that. 

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1 hour ago, IHAVEGAS said:

 

 

147 SNS truncated cone at 1.135 was what I was having the issues with. Went to 1.151 & have since run several thousand through 4 different CZ's with no worries, none of the guns have had their barrels reamed.

 

Have since switched from being a CZ nut to a being Tanfo nut, mostly, the Tanfo's like 147 RN at 1.15 and that seems fine with the CZ's also but I have not run lots of RN through the CZ's so I would not spike the ball on that. 

Glad to be of assistance 3 years ago!

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  • 2 weeks later...

Darn.  I loaded 147gr RN Blue bullets to 1.118 and still have the jam 20% of the time with IDPA slide lock reloads.  The guys at CGW said to load shorter and Rob at CZC said not to over-insert.  I am using mecgar mags which are flawless ... except from slide lock.  I am wondering if i should slow down my reloading and use the slide lock lever instead of counting on the auto-forward.  (I did file down the back of my slide lock so it will auto-forward easier).

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Update for me, had some recent occurrences even with my longer bullet seating, found that my extractor spring was worn and replaced it, also found a burr on the extractor edge that contacts the rim and smoothed that out.  Now, my CZ feeds fine, even with shorter factory cartridges.    Burr was found by running fingernail along the edge.  Spring is cheap.  I had been running the old spring under the mistaken theory that less pressure would let rounds slide up more easily, but I think it let them jiggle and occasionally jam.

I also had looked at brass case length mentioned above, but longer cases did not seem to correlate with jams.

 

For seating depth, load one every 5-10 thou up to maximum for mag (ex 1.169" for my gun with Xtreme 124gr RN) and slowly feed each to see what the sweet spot is.

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15 hours ago, bschulte said:

Darn.  I loaded 147gr RN Blue bullets to 1.118 and still have the jam 20% of the time with IDPA slide lock reloads.  The guys at CGW said to load shorter and Rob at CZC said not to over-insert.  I am using mecgar mags which are flawless ... except from slide lock.  I am wondering if i should slow down my reloading and use the slide lock lever instead of counting on the auto-forward.  (I did file down the back of my slide lock so it will auto-forward easier).

Are your rounds passing plunk test?

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  • 1 year later...

Yes, it passed plunk test.  What worked for me was putting in CZC plus 15% springs, (takes more effort to load magazine) and loading to an oal of 1.062.  I also filed very lightly and grease the connection between my slide and slide release so I get a consistent auto-forward during IDPA slide lock reloads.  

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