doublegunshop.com - home Forums General Discussion DIY Gunsmithing @ doublegunshop.com Zoli 12ga over .222 -- Rifle Headspace issue?

This isn't a gunsmithing project "yet" -- but it might become one....

I'm looking for some feedback on the image (below) of the flattened primers fired in the new-to-me (was bought used) Zoli 12 gauge over .222 Rem combination gun. The receiver is nicely engraved and the gun is in excellent condition, and as it came with the neat Valmet quick-detach rail-mount scope mount along with a decent low-power scope mounted on it (all for a really nice price) -- I'd really like to solve this issue and get the gun working well.

The 3 fired brass shown in the image all shot well -- grouping into 1/2" at 50 yards when using an informal rest.

The image shows (1) Hornady "Super Varmint" factory loading unfired brass, followed by (2) fired brass to the right. The bottom row shows (1) Remington factory load unfired, followed by (1) fired brass to the right. The primers of the fired Hornady brass look more flattened than the Rem brass, as you can see the rounded edges of the primer cups are more like sharp corners after firing; and the the primers cups on both makes of brass don't show the typical dimples that you'd see on once-fired brass -- and it appears the dimple has flowed back against the firing pin.

Since they're both factory loadings, I'd suspect this Bockbuschflinte has excessive headspace and it might become a "reloads only" project for me so I can adjust the brass to fit the chamber. (Luckily, I do load for the .222 Rem.) I could send the unfired & fired brass back to both Hornady and Remington for evaluation (as was suggested by a shooter at the range), but I don't think it's over-pressure -- and I'm more inclined to look at the lower .222 rifle's chamber first.

* Any other thoughts on the likely cause of this appearance of the fired brass?

* Should I also check the condition of the rifle's firing pin tip, or return spring?
(As it does drag on the fired brass and one shot was hard to open after firing.)

* Or, could the rifle hammer's spring be too weak?

Thanks!

Old No7

I don't know if excess headspace will cause flattened primers. The .222 headspaces on the shoulder and if there is excess headspace the case will stretch in length between the base of the cartridge case and the shoulder and, in extreme cases, can result in case head separation.

The firing pin tip may need refacing, there may be too much firing pin protrusion or the timing during opening of cocking may be off.

Thanks, this is what I've checked out so far...

* The gun has internal hammers with robust coil springs, just like you'd see on a Citori
* Both firing pins have nice, rounded tips; with the shotgun pin 1.5X or more the size of the rifle's pin
* There are no burrs on the firing pins, hammers or spring struts; all looks good inside the receiver (and looks well-made too)
* The firing pins do rebound, as they have to (to be pulled away from the breech so the barrels can tip down)
* The firing pins don't hit straight on as on a bolt action, but come in on angles from the side and elevation
* Unfired factory loads, with the extractor removed, fit flush to the breech face (so I don't think there's any excessive headspace)
* Neither factory bullet engraves the rifling when chambered; they sit flush but not tight
* Fired brass measures 0.002" larger than the unfired ammo just about the extractor groove (as several online articles say to watch out for brass that grows by 5 thous' or more (0.005") as being over-pressure loads_

Based on all this, I'm inclined to believe the primer flow is a function of the top-break design with the rebounding firing pins (which are pulled away from the breech face, as the pins sit roughly 1/16" below the face of the breech after "firing").

I'll try out some handloads which work well in my Rem Model 700, and using different primers, to see if the primer flow can be reduced any.

For sure, I won't be firing dozens of rounds with this gun.

Old No7

Excess headspace absolutely can cause flattened primers. I once experienced a complete head separation on a .22-250 Rem case because of it, and once is enough!

What happens during the milliseconds of the firing sequence is the firing pin pushes the case forward in the chamber until the shoulder contacts the front of the chamber. At this point, the case head is unsupported due to perhaps a few thousandths of an inch of excess headspace. The firing pin continues to drive forward detonating the primer. The charge ignites and rapidly reaches peak pressure. The brass expands and grips the chamber walls. The unsupported head is slammed back to the breech face (or bolt face), causing the brass to stretch where it becomes thinner just in front of the case web. (if headspace is really excessive, this can often be seen or measured if you section a case lengthwise). With old tarnished brass, you might also see a bright stretch ring after firing, just in front of the web. At the same time, the thin primer cup bulges out or begins to back out of the case. Then it is also slammed under full chamber pressure into the breech or bolt face, causing it to flatten.

This primer flattening can be severe even with loads that are well below an excessive maximum pressure. In the case of the two cartridges I fired just before the head separation, it would have been difficult to see where the primer edge ended, and the case began, except that the CCI primers were silver instead of brass. Extraction in a VZ-24 98 Mauser action was also difficult. Foolishly, I decided to try one more, and that was the cartridge that had the complete head separation. It felt like being violently being punched in both eyes, and I was totally blinded for roughly half an hour, until my vision slowly came back. For once, I had the range to myself, so there was no one to help me. A lot of shit goes through your mind when you are blinded. The wetness I felt on my face was blood, thankfully. At first I thought it was eyeball juice.

I had a strange vee shaped pattern of powder burns and brass particles surrounding my right eye. I learned a couple years later that Paul Mauser redesigned the 98 Mauser bolt shroud to deflect gasses from a ruptured cartridge between the shooter's eyes in that vee shaped pattern, and can attest that it worked... but I would not want to try it again.

I would suggest trying to find a gunsmith who has .222 Rem headspace gauges. You might have a chamber that is on the long side, but still in tolerance. So the factory load length brass could exhibit this symptom to a degree, since it must be sized to fit any factory chamber. In my case, I was given a set of dies and several boxes of brass that had been reloaded multiple times without annealing. I set the dies up to contact the shoulder of the old fired brass, which had apparently been used in a rifle with a minimum headspace chamber. Being work hardened, it was more prone to a separation, rather than simply stretching. When I later tried the exact same load using new unfired brass, I had no primer flattening to speak of, and extraction was easy. Of course, I tested the gun with the new brass by tying it to an old tire, and pulling the trigger with a long string, while standing behind a large oak tree.

Excess headspace can be due to a chamber that is longer than SAAMI tolerance, but it can also be created by setting up sizing dies incorrectly, and setting the shoulder back. So I would also suggest that you neck size only, or set full length sizing dies to barely kiss the shoulder of your fired brass. Your fired primers are nowhere near as flattened as mine were. I think the strange look of your firing pin indentations is due to the thin primer cup material flowing back into the firing pin recess, and then getting dragged across the holes when the gun is opened. I believe that is what caused your difficulty in opening too.

I do not fit firing pins on rifles that far below the breech face, .005" is plenty. The firing pin tip should fill the hole in the breechface, not allowing the primer to flow into the action in my opinion. That is how I fit high pressure falling block rifles to prevent the firing pin from binding and it works well.

Combination guns, especially double barrels (both SxS and O/U) pretty often leave primers looking like that because the firing pins hit on an angle (and casehead/primer pushes back at an angle to the firing pin) This displaces material the primer is made from to one side. I have noticed it often but don't recall it causing much problem. When the primer striking at an angle does cause a problem, the problem is usually misfire/hangfires. This is especially prevalent with old guns that used .254" Berdan primers and currently available ammo uses .217" Berdan or .210 Boxer primers. Current ammo that uses .199"(small rifle) primers is not likely to have ever been originally made with .254" primers.
Mike

Thanks all for your comments.

Old No7