Cz 527 7.62x39 Cures

Discussion in 'Gunsmithing and Repairs' started by highlander 5, Jun 28, 2015.

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  1. highlander 5

    highlander 5 Member

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    Mods move if in wrong place. I have 2 CZ 527s in 7.62x39 and had an on going problem that seems to be common and I thought that I would share my experience with others.
    The most common problem is these rifles will function fine with steel case ammo but not so well with comercial brass case ammo. First I tried replacing the firing pin springs,liked some brass ammo 20-30% would not fire even when struck twice. Tried handloads with a variety of brass cases full length resized still got misfires,tried neck sizing results not much better then full length sizing. Now I should mention I've 40+ years of experience in reloading. At my wits end I was poking around the various sites of reloading equipment and stumbled upon a set of shell holders of different heights from Redding to move the shoulder back that range from .002-.010 in .002 increments. Figured what the heck and order a set,used them as instructed and low and behold they worked. I loaded 20 rounds and all went bang on the first firing,I know this may not be a good sampling but before this I got 5 maybe 6 rounds to fire 2-3 miss fires and the pattern would repeat. I'll loading up a batch of 50 rounds with some cast bullets and see if my luck holds up.
     
  2. rcmodel

    rcmodel Member in memoriam

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    You can do the same thing by adjusting the sizing die to just bump the shoulder back enough for the bolt to close in the first place.

    No need to buy special shell holders when you can do the same exact thing with a proper die adjustment from the get-go.

    rc
     
  3. highlander 5

    highlander 5 Member

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    Tried that and I still got misfires.
     
  4. NINEX19

    NINEX19 Member

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    Oh, no... the CZ 527 in 7.62x39 has been on my short list for some time now. Seems difficult to find in person, I have found. In my research, I had not seen this as a problem people were having. Perhaps since the steel is so cheap and works all the time, people just stick with that anyway.

    Have you compared the dimensions of the common imported steel cased (which is what the CZ would have been made to use) stuff with the brass (domestic, I assume) cased stuff?

    How does the Hornady steel cased 7.62X39 function in the rifle? I am not sure of their case source, if it is made by them in house or they import it.
     
  5. rbernie
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    rbernie Contributing Member

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    Steel cased ammo normally has MORE recessed primers and needs more firing pin protrusion or shorter chambers to fire reliably. The cause of the backwards symptoms here has me confused at the moment.
     
  6. NINEX19

    NINEX19 Member

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    Yes, I am a bit puzzled too. If I understand correctly, perhaps you should try moving the shoulder forward and not back (if possible)? That would

    Do you have the same problem on reloaded brass cases that have not been resized, but are fire formed?

    Does this logic hold up? Not an expert, just thinking out loud.

    Brass and steel have very different metal properties. If drawing and sizing dies are made, based off of steel case dies or steel cartridge dies are pressed into service to form brass cases, this could force or allow the shoulders to be set at different places considering how easily brass flows compared to steel.
     
  7. atblis

    atblis Member

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    When you say neck sized, do you mean neck sized cases that were previously fired in that same rifle? If so, that's usually the recipe for nice accurate hand-loads in a bolt action rifle. The rounds should fit the chamber nicely. 7.62x39 is pretty heavily tapered, so it might benefit from a shoulder bump more often than other cases.

    I use and like the Redding competion shell holders. Simply note the particular shell holder for each gun and you have exact repeatability.

    Do you have a set of the Hornady comparators? I believe they would help you trouble shoot.
    http://www.midwayusa.com/product/479704/hornady-lock-n-load-headspace-gage-5-bushing-set-with-comparator
     
  8. highlander 5

    highlander 5 Member

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    I used a Redding neck size die for sizing cases and still got misfires. At that point I was stumped and stumbled across the Redding comp shell holders. The factory ammo I used was from Fiocchi and PPU.
    Even with a new firing pin spring I got misfires with Fiocchi but the PPU ammo fired 100%. Haven't tried Remington,Winchester,Federal (AE) or PMC as they are hard to come by as most shops carry the steel cased Russian ammo.
     
  9. highlander 5

    highlander 5 Member

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    Well an update over the last week and a half I've gone through 100 rounds of various handloads and 50 rounds of factory ammo and no misfires so it looks like the Redding shell holders were the answer to my problems. Thank you all who made observations and suggestions.
     
  10. atblis

    atblis Member

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    I wonder if it has something to do with the rims and the way they're held to the bolt face. If headspace is a little loose because the shoulder is being set back too far, the rim geometry might have an impact on how the primer is hit by the firing pin. I kind of doubt this because neck sizing only apparently didn't work.

    I'd measure how far the firing pin protrudes from the bolt face. I suspect it is a little short or there was something preventing it from travelling as far as it should.
     
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