Custom gun Blowing primers/headspace problem?

axialmillipede

axialmillipede

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Hello,

I'm hoping to get some opinions for a friend that recently had a gun built and is having problems with it. he only shoots factory ammo, he does none of his own reloading. So he gets it home, and it's blowing primers out of factory ammo. The firing pin is piercing the primer. The fired cases were also starting to have a visible bulge at the case head. So I took a look at it(being an aspiring gunsmith) and I just happened to have a set of go/no go gauges for this particular cartridge. The bolt easily closed on the no go gauge. We measured his fired cases with a hornady head space comparitor, and they were about 4 thou longer than what my new no go headspace gauge was.

So I gave him the gauge, and told him to bring it back to the gunsmith, and ask why his gun would close a bolt on a no go. The gunsmith told him that it was his ammunition, not the chamber. And that they used a different brand of head space gauge and reamer from why I had given him to check. And that you can't use brand X no go gauge when the chamber was cut with brand y reamer.

This is the first time I've heard of this, but I'm not a gunsmith. I assumed that a headspace guage was a headspace gauge, and that they should all be manufactured to the same length, regardless of who you buy it from.

To give some background, the exact same gunsmith did the exact same thing to me a few years ago. They cut the chamber too deep and told me it was my reloading when the primers were flat, and the brass was visibly bulging. I took in some factory ammo that did the same thing, and eventually they ended up re cutting the chamber.

So I'm trying to educate myself, and help a friend. Any opinions would be welcome.
 
Sounds more like a gunhack than a gunsmith.

Gauges are supposed to be made to a standard dimension/spec, brand isn't supposed to matter if its made correctly.
 
I'd also like to add that the bolt closed snug on the no go. He said it was okay because you had to force it a bit to close the bolt. I was kind of under the understanding that bolts shouldn't close on a no go at all. Period. Ever. If the bolt closes on a no go, the chamber is too long. No matter what brand of no go, or how much force.
 
axialmillipede said:
I'd also like to add that the bolt closed snug on the no go. He said it was okay because you had to force it a bit to close the bolt. I was kind of under the understanding that bolts shouldn't close on a no go at all. Period. Ever. If the bolt closes on a no go, the chamber is too long. No matter what brand of no go, or how much force.
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This is correct. He cut the chamber too long or at least out of spec. I'd be looking at another gunsmith and lose this guys phone number. Time to tell your friend to cut his losses before he screws up a gun so bad, it can't be fixed. The gunsmith was educated at Bubba's gunsmithing Emporium.
 
Headspace gauges are made to an exact tolerance, regardless of make. If you feel a stripped bolt close on a no go gauge... it is within acceptable tolerances but I would prefer it be 2 thou tighter. Keep in mind 5 thou tighter and you would not close on a go gauge...

Headspace does not cause the primer failure you are experiencing. Primers don't get pierced by the firing pin, they blow outwards due to a poor fit of firing pin to firing pin hole and/or a weak firing pin spring and/or excessive pressure. Being factory ammo it would require an extremely short throat to get the pressure up.

From what you have described this is the second time around with this fellow... is he a friend or are you a slow learner?
 
I mean...a new gun blowing primers with factory ammunition?!?! It just doesn't seem right to me. Letting a gun like that go out the door seems like a good way of seriously hurting someone. Then bringing it back and not owning up to the mistake makes it even worse.

Also they were saying that the superduoer match grade and varmint ammunition runs at higher pressures. Correct me if I'm wrong here, but shouldn't all ammunition be under the saami maximum pressure?? Any available ammunition should fire safely in any gun. Isn't that the point of saami specs?! Making sure headspace, chambers, and pressures are all standardized to keep people safe??
 
And for the record, I've heard and seen enough horror stories with these guys, They'll get none of my business ever again. I'll admit, I got sucked into the local hype that they walk on water.

Screwing up my chamber was strike one

My cousin got a 7mm built, and they bedded it so crooked in the stock, it has 1/8" gap on one side of the barrel and is rubbing on the other side. Strike two

Another friend had a muzzle brake put on, and they made it too small, it was shaving bullet jacket off and spitting at by standers. Strike three

And now this guy makes strike four.

How they haven't killed someone with this level of quality control is beyond me.
 
axialmillipede said:
I'd also like to add that the bolt closed snug on the no go. He said it was okay because you had to force it a bit to close the bolt. I was kind of under the understanding that bolts shouldn't close on a no go at all. Period. Ever. If the bolt closes on a no go, the chamber is too long. No matter what brand of no go, or how much force.
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I wouldn't go straight to period or (not) ever. A head-space gauge is a tool of feel, not force. If you can feel some resistance with a stripped down bolt the gauge is touching and that is all its supposed to do. We live in a plus or minus world and anything between go and no-go is GTG. Even then, a rifle is serviceable until it will close on a field gauge. Maybe not great, but you set your dies and life goes on.

None of which changes that the gunsmith screwed up somehow. I have a rifle here that in its earliest incarnation was put together by a western shop. It was so loose that it would close on a field gauge and the primers looked like hub-caps. I wouldn't take a dog there to be shot.
 
Ask that "gunsmith" if he knows what SAAMI is and what it does? Factory chambers are all spec'd to specific tolerances and the make of reamer and headspace gauge is entirely irrelevant. All must conform to the SAAMI spec.

My suggestion is you don't use that particular "gunsmith" anymore.

I have a feeling I know who you are talking about but I am legally prevented from saying anything further.
 
Blowing primers is not caused by headspace. Bulged cases are not caused by headspace. It would seem that the rifle, as described is a little long in headspace but not dangerously so.
 
Be curious to know what caliber. The only one I could possible think of that may have that issue and even that Im not sure about would be a 6.5x284 with the chamber differences or gauge differences from the Lapua, Winchester, and Norma. Seems like there just werent a lot of f*$cks given when working on it. I would find a different builder to set back the chamber and fix it up. There are several good people to work with in Alberta.

Also be curious to know who it was. Not sure why it would be a "legal" issue to say who did a shoddy job a couple times. Isnt that why we have a forum, to praise good work and to warn other gunnies of bad practices?
 
axialmillipede said:
I mean...a new gun blowing primers with factory ammunition?!?! It just doesn't seem right to me. Letting a gun like that go out the door seems like a good way of seriously hurting someone. Then bringing it back and not owning up to the mistake makes it even worse.

Also they were saying that the superduoer match grade and varmint ammunition runs at higher pressures. Correct me if I'm wrong here, but shouldn't all ammunition be under the saami maximum pressure?? Any available ammunition should fire safely in any gun. Isn't that the point of saami specs?! Making sure headspace, chambers, and pressures are all standardized to keep people safe??
Click to expand...


What kind of chamber was cut a match chamber or a saami spec chamber there is a big difference if using factory ammo and might be the cause of excessive pressure if a saami chamber wasn't done .
as far as the bolt closing on a no go gauge with some resistance sounds to me like the headspace is within specs gauges can vary a little bit there are tolerances + or -and forcing a bolt to close on a gauge is not recommended any resistance means it is a no go.
 
If i No Go closes with a stripped bolt with more than the touch of a finger and you can feel the bolt binding on it, its right at the limit, but id say its still within spec for a standard gun. head space is measured in thousands of an inch, as guntech said, 5 thou .005" can go from a no go closing to a go not closing.

Blown primers would not happen on a over head spaced gun as you are describing, the primer would visibly be popping out of the primer pocket, Pierced primers would be either a problem with the firing pin, or over pressurized loads.

For a match grade gun that was going to be shot with hand loaded and sized ammo, id want the nogo to be a solid stop when trying to close, a hunting gun that would be using various factory ammo, a tight close nogo would be preferable as each company has slightly different tolerances for their ammo.
 
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