Cz 527 firing pin protrusion

[Stubby]

I've had an issue. During load development, I pierced a primer at 23.8 grains of 8208. No real other pressure issues. Slightly flattened primers. Found acceptable accuracy at 23.3 and loaded a bunch up. During final sight in, it shot ok, but after 5 rounds pierced another primer. Remington 7.5 primers, Norma brass, 25 grain hornady hp. Any ideas what could cause the pierced primers? Cz usa tells me that .205 of firing pin protrusion is normal. Anyone have any input? It seems like it would be too much protrusion, and it's piercing primers randomly. Well below max powder 17 rem

[greasemonkey]

Using Norma brass you need to back the powder down. It doesn't have the capacity as Remington. My CZ 527 17 rem using 22.5 of 8208 / 25 hp's was over 4200 fps and popping primers also. Found a load with H4895 21.5 grs running right at 4000 with Norma brass. Most of the book loads are based on Rem brass.

[georgeld]

Is the pin tip smoothly rounded?

Be careful with these small cases.
Just because they're real small don't
mean the pressure isn't still way up there.

I blew a gun up with just 10.2gr H110 in a NEF rifle
and 5.7 case necked to 17.

Study the burn rate charts and try to know what you're
doing ahead of time.

Wear eye protection you've only got two of 'em!

[flyrod]

Originally Posted by georgeld

Is the pin tip smoothly rounded?

+1

Once you get a pierce the pin usually gets eroded or cut by gas and the problem gets worse. The 527's I've seen had oversize firing pin holes in the bolt face, which also makes this problem worse.

I would suggest primers with thicker cups, like those made for the gas guns. I think CCI #41 BR4 and 450 are supposed to have thicker brass.

Also, I don't know what you mean by .0205 but protrusion should be around 1.5mm and I think the pin stops on the receiver so it's not trivial to measure.

[Bill K]

I would suggest primers with thicker cups, like those made for the gas guns. I think CCI #41 BR4 and 450 are supposed to have thicker brass.[/quote]

Are not 7.5 Remington primers listed as among the thickest cup primers ?

[TinMan]

Per my info, The 7.5, the BR-4 and the 450 all have the thicker cups.

I would suggest disassemble the bolt and clean out any debris from the primer, and check if the is any other damage. Maybe that lot of powder is a tad hot. Back down the charge.

[Daryl]

A chronograph can be your friend. If the velocity is too high, that should tell you something.

[Bayou City Boy]

Go to the link below and look at the "Informative Articles" and find "Primers and Pressure" There you'll find a chart comparing primer thickness, etc.

http://jamescalhoon.com/

Also with a chrony being your friend, if you have a workable and safe load, as you add another increment of powder - for example one more 0.1 grain of powder - you will see an incremental increase in muzzle velocity. When you add powder and you don't see the increase in velocity, you've probably gone too far and need to back off on the powder charge to be safe.


-BCB

[Stubby]

I edited the original post. Pin protrusion, as I can measure it, is .205. I measured it by unlocking the pin by twisting the rear of the bolt where the firing pin screws in.

[flyrod]

Originally Posted by Stubby

Pin protrusion, as I can measure it, is .205.

I'm guessing you're talking inches? As I mentioned above, I don't think you can measure it the way you did. I think in the 527 the pin stops against the receiver, not the bolt. With the bolt out of the receiver the pin can travel further.