CZ 527m Over Pressure Problem

[Piotrowski]

I bought some new Winchester brass (7.62x39) for my Carbine and have been (nearly) blowing primers with every shot.

Thought it might be a hot new batch of H335, so l broke down those loads and created a few more rounds with a light load of 1680. Didn't shoot more than one because of a blown primer again.

The brass doesn't measure as out of spec. I'm using the same Hornady FMJ bullets at 2.200 and the same WLR primers that I've used in the past.

I did a real thorough cleaning on the off chance that a carbon ring might be the problem and that did nothing.

This is the first time in years that this rifle has given me any problems.

Any ideas?

BTW. Tulammo shoots fine. Also pushed some bullets in to 2.185 as that's what the Tulammo COAL measures but haven't fired one yet.

 

[asauer]

How did the primers feel when seating? If factory ammo shoots fine without pressure signs, it sure isn't the gun.

Let me ask what exactly you're having an issue with- are the primers leaking gas around but staying put, or are they falling out when the case is ejected?
I'm also assuming you've used these primers on other calibers/brass, so they are not suspect?
If primers felt tight going in, primers are known good, and you're using a starting load, the brass is junk.

 

[Piotrowski]

Primers are from a batch of 5000 that I've been using regularly. Primers went in fine; none of them felt loose. After ejecting the rounds, the primers were partially popped out.

When I fired the one round of 1680, I knew I was going to see the same problem because the rifle felt like it kicked a bit harder than normal.

(Commenting again that the only things different were a new lot of H335 and the Winchester Brass. I went back down to the starting load with the 1680.)

I think I'll try reloading the once-fired brass (assuming that the primer pockets aren't blow out and loose now) to see what happens. If that works, maybe I'll just fire form the brass with a really light load and go on from there. I may also contact the dealer to see if anyone else is complaining. I doubt they let me return it.

 

[MQ1]

Triple check your scale.

MQ1

 

[asauer]

The primers were backed out ? As in not flush? But still retained in the case?

 

[flatlander]

Yeah, backed-out primers makes it sound like it could be a headspace issue with the new brass. Check the un-fired headspace of some of that brass compared to that of a fired case from the previous lot of brass you were shooting using something like a Hornady Lock-'n-Load Headspace Gauge. If the new brass is several thou shorter in headspace, that could be your problem.

 

[Macropod]

Are you using .311-312" projectiles in a 0.308" bore?

 

[asauer]

Not saying that couldn't be the problem here, but I've done it and no issues.

I agree on checking headspace as said above. Sounds like your new brass is very short from case head to datum line on the shoulder.

 

[Eric Leonard]

I am pretty sure the CZ 527 has the .311 bore,,,I know a couple people that shoot the 174 SMK in theirs,,

 

[wapiti25]

check the diameter of the flash hole. larger flash holes will change the pressure.

 

[Piotrowski]

Thanks for the replies...

Read this at the Redding website:

"So how do we know when we have too much headspace? There are a couple of obvious tell tale signs on our fired cases that are sure fire indicators. The first is a protruding primer. If, after firing, you see the primer is backed out of the primer pocket, even a little bit, you have excessive headspace. Remember, the top of the primer in an unfired case is supposed to be located just below the case head after it has been seated. If it's sticking out after the shot has been fired, the case is too loose in the chamber."

I do think this is the problem as it happened with a round that I shot this morning that had a really light load. Hopefully, fire-forming the brass and making sure I don't push the shoulder too far back when reloading will resolve the problem. (I'll probably find out tomorrow.)

 

[Piotrowski]

L-R: Russian steel case, Winchester once-fired, Winchester new.

Seems like a real obvious change in shape of the brass after firing, but it still doesn't look like the shoulder has the same shape as the steel?

What I've heard is that CZ designed the chamber to handle the cheap Russian ammo with more accuracy than you'd expect from an AK. Raises the question as to whether the brass will be stretched too much by the time it takes on the shape of the Russian case?