Failure to detonate-even after being sent back to cz

[falup]

friend has the 7.62x39 rifle. cleaned & polished again after getting it back from cz. there are pin marks on the primers
            but, becomes erratic after a dozen or more shots.
            he's getting pretty discouraged. it shoots about moa w/
            non wolf surplus.
            anyyone with experience?

[Fred Flinstone]

Whitout pointing the finger to anyone or anything: have you tried any other ammo(since you're presently shooting surplus which is why the country of origin got rid of the stuff: possibility of misfire, if these are handloads the primer may have come in contact with oil or other contaminant.
           
            After all this has been checked: I would recommend changing the firing-pin spring by a Wolff high-tensionned one(this will also give you a quicker lock-time), before re-installing the firing-pin look at it for any drag mark, burrs, excess shavings etc. Just to be sure polish it. Test it without spring tension, is it free? If not polish the firing-pin channel.
           
            My deep feeling is pointing to your ammo.

[falup]

forgot to add- when this occurs the firing pin,1st & 2nd ones,
            are barely through the bolt or stuck. supposedly also had a new test fired bolt  assy put in at the factory.

[Fred Flinstone]

You can make a quick easy test, dismantle bolt and firing-pin mechanism. Insert firing-pin by hand in the bolt, is the tip of the firing-pin protruding(enough to cause ignition?):
            1- If not something is blocking the movement(firing-pin burr, nick,etc. or within the bolt where the firing-pin is suppose travel)
           
            2-Check if travel within the bolt is blocked by a foreign object. De-lubracate every part to make sure any foreign object is not hiden within the gun grease.
           
            3-Take firing-pin & insert it from the front: pointy part of firin-pin ponting toward(where it's usualy pointing out) the rear of the bolt as to determine if firing-pin has been baddly machined,
           
            I would seriously change the original firing-pin spring for a Wolff gunspring(take the highess tensioned one, not the same value as O.E.M.), CZ springs are not my favorite to say the least. Another CZ rifle shooter was writting to me on another CZ spring problem, 1+1=2

[falup]

Good news- serious polishing of the  pin & slight opening up of the hole appears to have solved the prob.
            FF- the wolf overpower replcmnt spring is a common fix for a lot of guns & mags anymore. seems to be a bad trend that is widespread. Sounds like the bean counters are undermining
            some good engineering designs.
            thanks.