Question re. bulged primers

[olyinaz]

I have a 9mm carbine, a MAC clone (semi - fires from the closed bolt), which is exhibiting bulged and cratered primers on some brands of ammunition. Specifically Remington standard bulk 9mm hard ball. Winchester white box less so. Federal bulk pretty much no bulged primers, but most pretty cratered as with the Winchester. I'm not bump firing. I'm not rapid firing. The rest of the case looks fine but they're all pretty sooty.

The other thing I notice is a pretty healthy puff of gasses upon ejection of rounds about 50% of the time. Nothing "hot" feeling. No stinging bits to the face. Just puffs my hair up a bit sometimes.

Again, the brass looks fine - no bulges and I don't see how out-of-battery could be an issue since this is a closed bolt gun and these are slow fired shots.

Thank you for your feedback and info guys! And YES, I did research this as much as I could already using Gargle - most of what I found had to do with bump firing etc. Not my bag! I just need to know what, if anything, is wrong with this carbine.

Thanks!

Oly

[RSY]

Sounds like the headspace may be a tad too large or a long cut chamber. Are the primers also backing out (or, is that what you meant by "bulging")?

Scott

[Terry Murbach]

THERE IS A HUGE DIFFERENCE BETWEEN " CLOSED " BOLT, AND LOCKED BOLT !!

[olyinaz]

THERE IS A HUGE DIFFERENCE BETWEEN " CLOSED " BOLT, AND LOCKED BOLT !!

Yes, I know that Terry, but since I had stated that it was a MAC clone I wanted to make the point for information before someone suggested an open bolt issue.

It is a simple, unlocked, mass-delay blowback operated 9mm carbine. The rounds I was shooting were standard pressure (no +P or "carbine only" types).

Your reply is typically unhelpful and as I stated, I tried to research the issue before coming here for some opinions/feedback. If your reply was meant to point to something, some specificity would be reasonable. If cases looking like mine are typical for this kind of firearm I need to know that.

Oly

[olyinaz]

Sounds like the headspace may be a tad too large or a long cut chamber. Are the primers also backing out (or, is that what you meant by "bulging")? Scott

No, the primers are not backed out at all. I do suspect that the chamber is pretty roomy given the soot on the rounds.

I took some photos of a case with my trusty iPhone. I hope that these will help with diagnosis:







Thanks again to anyone who can shed some light on this before I go to the trouble of packing it off for the local gunsmith to look at. I suspect that a combination of a chamber on the wide end of spec and a reciprocating mass and action spring a little on the light side lead to this. What I'd like to know is if it's dangerous and if it requires fixing.

Oly

[harry]

The R&P case in the picture has a very bulged case to go with the primer, the primer showes that the bolt is moving and causing head space issues with those rounds.
Harry

[wecsoger]

Had a Cobray M11/9 that exhibited essentially same behavior. Smoky cases, yes. Don't recall the bulged primers, but they did flow back around the firing pin. On bad days it had a terrible trigger slap also.

It had enthusiastic ejection so that's what I chalked up the smoky cases to - the brass never quite got to sealing up the the port before it was yanked and cranked over the side.

Is it an artifact of the camera or lighting or is there a noticeable bulge on the left side of that case? Can you roll them on a piece of glass to see if they're out of round?

But yeah. If those are the only ones bulging, I'd put it in the same category as, "doctor, doctor, it hurts when I do this" and not shoot them.

Fun for making noise, but not the acme of the gunmaker's art. I'd mount a fluorescent green bayonet on it and sell it off to someone in the zombie preparation bunker crowd.

[RSY]

Is the hole for the firing pin in the boltface excessively large? That donut around the strike is bizarre...to me, at least.

[Mescalero]

I would seek professional help.
None of that looks good to me, sorry I have no direction for you other than that.

[AJMD429]

Is the hole for the firing pin in the boltface excessively large? That donut around the strike is bizarre...to me, at least.

Yep, that is strange.

Your PHONE takes better close-ups than my (old, but) fancy digital camera...

I wonder if the issue could be a thin-walled primer (could you somehow deprime a couple cases and measure the cup thickness before firing, vs. the other primers). I say that because you report it only occurring with one type of ammo.

The other issue Terry could have been so eloquently and delicately referring to would be that if it isn't a 'locked' bolt, but rather a 'closed' bolt, even with slow-fire, the bolt could conceivably start some rearward motion while the bullet it still in the bore, and if the brass gripped the chamber better than other brands (or the bullet/velocity differed enough), the pressure could be blowing back the primer before the brass starts to move. That could be due to stickier brass, different ballistics/load, or thinner primers that are more prone to showing the ill-effects of all that.

[olyinaz]

Had a Cobray M11/9 that exhibited essentially same behavior. Smoky cases, yes. Don't recall the bulged primers, but they did flow back around the firing pin. On bad days it had a terrible trigger slap also.

It had enthusiastic ejection so that's what I chalked up the smoky cases to - the brass never quite got to sealing up the the port before it was yanked and cranked over the side.

Is it an artifact of the camera or lighting or is there a noticeable bulge on the left side of that case? Can you roll them on a piece of glass to see if they're out of round?

But yeah. If those are the only ones bulging, I'd put it in the same category as, "doctor, doctor, it hurts when I do this" and not shoot them.

Fun for making noise, but not the acme of the gunmaker's art. I'd mount a fluorescent green bayonet on it and sell it off to someone in the zombie preparation bunker crowd.

Hmm, that's interesting. Thanks. The issue is so common with MACs that I wonder why they don't just put stiffer recoil springs in the dang things...

Well, at any rate, the cases are indeed bulged just a bit, but I've got other 9mms (and some lever guns) that do it worse and most of what you see is an optical illusion due to camera angle and focal length etc. Not out of round, just fat around the mid section a bit.

I'll take it in and have it looked at tomorrow.

Oly

[olyinaz]

Is the hole for the firing pin in the boltface excessively large? That donut around the strike is bizarre...to me, at least.

Yep, that is strange.

Your PHONE takes better close-ups than my (old, but) fancy digital camera...

It's amazing no? I love the dang thing. It's so nice to have a GOOD camera with me all the time. It even takes HD movies...

I wonder if the issue could be a thin-walled primer (could you somehow deprime a couple cases and measure the cup thickness before firing, vs. the other primers). I say that because you report it only occurring with one type of ammo.

The other issue Terry could have been so eloquently and delicately referring to would be that if it isn't a 'locked' bolt, but rather a 'closed' bolt, even with slow-fire, the bolt could conceivably start some rearward motion while the bullet it still in the bore, and if the brass gripped the chamber better than other brands (or the bullet/velocity differed enough), the pressure could be blowing back the primer before the brass starts to move. That could be due to stickier brass, different ballistics/load, or thinner primers that are more prone to showing the ill-effects of all that.

I suspect that's true regarding what he was getting at (big assumption...I'm not a mind reader) but it just doesn't seem to fit - the primer is not backed out at all. Others are cratered pretty heavily but not domed like the example in the pic. That the hole around the firing pin is "generous" seems pretty hard to dispute. What I don't get is how you wind up with that dome on the primer.

The only other gun I've ever seen do this was a friend's 9mm Tokarev, and that gun has a locked breach.

Oly

[AJMD429]

Perhaps a factory-sealed primer would bulge before backing out, especially if it were of thin-wall construction...?????

[Thunder50]

Possibly weak recoil spring and check the firing pin hole to see if it is wallowed out a bit

[Cliff]

Interesting discussion. Looks like an enlarged firing pin hole and a possible weak firing pin spring if it has one. The first thing that moves upon firing is the primer. They will set back, John Garand, used this feature on his first design for his rifle the M1-Garand, had to reengineer it when the military went to crimped in primers due to primers backing out in machine guns with improper head space. He went to the gas system to unlock the rifle. If you can get your hands on a copy of Phil Sharpes "Complete Guide to Handloading", he did a lot of work on head space, using different machine guns. I don't know if he mentioned bulging primers but he did find primers could fall out with improperly head spaced barrels. He would unscrew the barrel a bit at a time recording what was happing in doing so. He went through a big bunch of G.I. Ball which was provided by the Military at the time. Also look in "Hatcher's NoteBook" he also did a lot of experimenting on whether or not excess head space could cause malfunctions. If there is no spring on the firing pin (ala Colt's Govt. model) maybe increase spring power on hammer or striker may aid in resolving the problem. ATB

[olyinaz]

Possibly weak recoil spring and check the firing pin hole to see if it is wallowed out a bit

Well that's what I've been suspecting, but it sure is interesting to hear other opinions.

Oly

[olyinaz]

Interesting discussion. Looks like an enlarged firing pin hole and a possible weak firing pin spring if it has one. The first thing that moves upon firing is the primer. They will set back, John Garand, used this feature on his first design for his rifle the M1-Garand, had to reengineer it when the military went to crimped in primers due to primers backing out in machine guns with improper head space. He went to the gas system to unlock the rifle. If you can get your hands on a copy of Phil Sharpes "Complete Guide to Handloading", he did a lot of work on head space, using different machine guns. I don't know if he mentioned bulging primers but he did find primers could fall out with improperly head spaced barrels. He would unscrew the barrel a bit at a time recording what was happing in doing so. He went through a big bunch of G.I. Ball which was provided by the Military at the time. Also look in "Hatcher's NoteBook" he also did a lot of experimenting on whether or not excess head space could cause malfunctions. If there is no spring on the firing pin (ala Colt's Govt. model) maybe increase spring power on hammer or striker may aid in resolving the problem. ATB

Firing pin or hammer spring? Hmm, these things reportedly have extremely strong hammer springs, and I guess you're telling me why? That is definitely something to look into.

Oly

[Griff]

That has the appearance of an "out-of-battery" shot. To me, it looks like the web of the round is not being supported at ignition. Have you measured one of those fired cases & compared it to an unfired one? Either the chamber is over-sized or ? Have it professionally checked. I ain't up on foriegn rounds... Is a 9mm Luger the same size as a 9mm Parabellum? I'll go and look that up, but, it's quite possible I'm wrong. But, before I'd shoot that again, I'd elliminate that as a possibility.

Methinks Terry is more knowing than he's lettin' on. Remember, sometimes being told the answer can be a disservice... hereas following clues can yield permanent knowledge.

[Griff]

Ok, they are the same. What's the Difference Between 9mm Luger and 9mm Parabellum? But, please note: "Some military ammo is loaded hotter, and/or with harder primers, for use in submachineguns. Such ammo should be avoided for use in your average 9mm pistol." It doesn't say what happens when you fire thhe std. ammo in a subgun.

I still say it looks like an "out-of-battery" shot.

[Ben_Rumson]

Dunno anything about your carbine’s bolt design but it looks like the bolt face may have a firing pin bushing that’s setting back if the bolt does indeed have one. As for the case the soot is on the same side as the bulge so that’s a normal chamber/case fit issue..

[Ben_Rumson]

Oly... Any updates?