CZ527 7.62x39 Failure to consistently fire CHICOM ammo

[Guest]

Don't know the ammo or the calibre but I have a few CZ 527's and never had an issue with the firing pin.

Is this old ammo and would it possibly be the ammo fault or rather primer fault.

When you said older I'm wondering if it's the corrosive primer material type before they switched to the lead based sealed primers which don't contaminate.

[Mega]

Don't know the ammo or the calibre but I have a few CZ 527's and never had an issue with the firing pin.

Is this old ammo and would it possibly be the ammo fault or rather primer fault.

When you said older I'm wondering if it's the corrosive primer material type before they switched to the lead based sealed primers which don't contaminate.

[Mega]

Sounds like an interesting Calibre, just read up on it's history.

Reading between the lines, I'm taking it that the ammo is old.

I would really be suspecting the Primers and perhaps not being sealed have created the problem. Maybe mass produced millitary ammo that really leaves quality control as an issue in times gone by. Pity there isn't a way to just replace the Primer but that would affect the whole load tune too.

Hope you get someone that has first hand knowledge.

[Mega]

Oh....!!!!!!

I think you answered your own question.

How much "Headspace" does it have. Do you have OAL Case Gauges to measure an "Unfired" to "Fired" round .... The thing I'm thinking of here is if the firing pin isn't long enough for a proper strike irrespective of how strong the spring is.

If there is a lot of case length expension after being fired it would indicate way too much headspace. The only solution if that is the case would be to reduce the headspace but with a CZ that's a permanent adjustment. Something like a Savage where you can wind the chamber back to reduce headspace perhaps but no sorry no other ideas. Really sounds a bit on the hairy side.

[Mega]

Not sure if that will tell the whole story but .....we'll see.

Do you have Calipres and do you have something like a Nut that will slide over the neck and 85% down the shoulder if you don't have an OAL Gauge. Measure the Base to back of that say "Nut" sitting on the shoulder of both an unfired and fired round and read the difference.

Just a thought.....

[S12A]

Gday AC

have you looked at primer hardness as a posibility?

it may not be that they are faulty but commercial ammo has a lot softer primers than some surplus stuff.

They look the opposite to me...the ones that fired are too deep.

Taking into account AC has installed a STRONG Firing Pin Spring and I think TOO strong... If it hit any harder and deeper he would be piercing primers and cause another major drama....

Sorry, I was answering S12A but the quote wasn't inserted......

[Mega]

Double post....

[Mega]

I can CERTAINLY see an issue.......

The fired cases have a huge firing pin creator, that's a BIG strike. BUT, compare to those that didn't fire and there is a HUGE difference that I can see to the depth of strike.

NOW ....

Two things.... First I think the strike is TOO hard but I also think the whole Cartridge might be moving forward in the chamber as it's hit by the firing pin so hence some hit n miss firing.

Second, the Unfired one's look to me taking into regard the first issue that the Firing Pin Hit is soft.... the Head Space is buffering the blow by the case movement and not effecting a fast enough hit to ignite the prime. Once hit the "Anvil" may have moved forward therefore killing any further attempt at firing the primer.

I take it that you know how a Primer works.... that little dab of Nitro that gets the percussion and goes kaboom....joke mate.... but if it doesn't have the space for the strike it won't go off... unless you hit it with a hammer.

If you have so much ammo and it's really worth it then yes ..... Get a chamber reamed short so you can use this ammunition but realise you can't use anything longer.... The good news....you can always have the chamber reamed longer so late you can use the proper if that exists length ammo.

Does all that make sence.....????

I'd love to be able to measure all those cases and I think I'd have the problem solved.

BTW...when you do solve it ... I'd be changing the heavy firing pin spring back to the original .... I think that will cause further issues.

[John23]

Just a thought in regards to the excessive head space theory.

How do you feel about using an factory case (bullet pulled) as a gauge?
Put some layers brown packing tape (0.001" thick) on the back of the case and find the point where the bolt wont close.

One thing I found when comparing fired to unfired cases to determine headspace is you need to take averages.
Measuring virgin lapua brass I found there was up to 0.005" variance in the position of the shoulder.
I also discovered that it took a few firings to get all the cases to the same length.


JH

[Mega]

THIS COULD BE DANGEROUS ..... ?????

What about packing all your cases before firing so they are all pushed forward by the bolt and take out the slack from a loose headspace.... Thinking, thinking .... maybe not such a bad idea since your have such a strong strike.... maybe, maybe try one .....

Then again it may leave bits of tape on the Bolt Face or in the Chamber....

Just a wild thought.

[John23]

Pulling the bullet and using a case is the safest bet.

I will edit my post as although it may work it probably is not a good idea to be chambeing live rounds unless the intending to fire them,

JH

[Mega]

It may be less dangerous than what's going on at present if excessive headspace is your problem.

I even thought of adding a spacer, metal, to the front of the bolt face whilst you are using these rounds.

Really, do you know a Gunsmith, I'd give him a ring especially if you can determine that they are in fact too short.

Easy for me to say because I have a friendly Gunsmith that doesn't mind a yarn, then again if I drive an hour will do little jobs that take no time whilst one is visiting....not often but it happens. If I went to the Range more often I could have it done there.....but at least discuss and look.

[John23]

Interesting and cheap fix to excessive head space Mega.
I would be interested to see if it would work. Much less of a job than removing a barrel and modifying the length of the shank.

What I referring to with the tape was to only determine if the headspace was excessive.
If you can not close it bolt with 1 or 2 bits of brown packing tape on the case you will have good headspace of 0.001" to 0.002" give or take.
If you are up to 3- 5 and so on bits of tape and still closing the bolt you have excessive headspace. (assuming your cases are the correct size)

The only real way in my opinion to get a exact result would be to purchase a headspace go gauge and then follow the tape trick again.


Using a new unfired case is a good cheap place to start anyway,


JH

PS

Its just probably the old crappy ammo that is causing the problem.
Mountain out of a mole hill it has become.

[Mega]

At least try the measurements yourself and see if you can isolate the issue.

If it goes to the Gunsmith then don't forget to take the Ammo with you and make sure he is aware it's live ammo. Probably also some fired cases so he can gauge for himself and get it right.

As I said, later down the track if you are using newer, longer ammo it's a simple job to ream the chamber slightly longer. Probably 5 minutes as they do it with a hand held reamer holder....no need to set up the Lathe .... if it's only a few thou. Been there, done that.....

All the best with it.