Bullet diameter tolerance?

[turbo54]

A friend uses 162 amaxes in his 708, over 45.5gr H4350. It is the only rifle cartridge he loads.

This load works very well with no pressure signs.

He recently bought 162amax "blems" from midway. At the range, he had a few cartridges "push a button", and one blew a primer as well as REALLY pushed a button.

I don't believe you can fit enough H4350 into a 708 cartridge loaded with a 162 @ 2.830" to be "grossly" overpressure like this.


We mic'd 100 bullets from the lot and found:

86 bullets measured .2840"
10 bullets measured .2839"
4 bullets measured .2841"
1 bullet measured .2842"

Does this seem reasonable?

Is .0002" oversize capable of causing gross overpressure?

 

[melloyello]

That diameter difference isn't even worth mentioning.
Were cases FL resized? If not, how many times have they been shot without FL resizing? How many times fired total? Same primers as usual? Was the cartridge temperature hotter than normal? Gun recently cleaned?

 

[turbo54]

Cases are FLSd each time. He sets his die correctly for a .002-.003" bump. Cases have been fired 4-5 times. Same primers from same lot as always. Powder from same lot. He's got about 1000 rounds down the pipe with this load with no issues yet, and sometimes at higher ambient temperature. The rifle had been cleaned prior to this outing, but it had ~100 rounds through when it blew the primer.

 

[mahbin]

Was there any oil left in the chamber after cleaning, that will make it have pressure signs?

 

[Temp9]

How close was he to the lands? If he was really close (like .010" or closer), the new lot might have varied just enough to touch or jam into the lands. That would give a pressure spike like he saw. What other pressure signs were present?

 

[Advokaten]

I would look more towards the barrel, your friend might have slight copper build in his barrel, causing massive pressure spikes. /Chris

 

[turbo54]

Was there any oil left in the chamber after cleaning, that will make it have pressure signs?

No.

How close was he to the lands? If he was really close (like .010" or closer), the new lot might have varied just enough to touch or jam into the lands. That would give a pressure spike like he saw. What other pressure signs were present?

His chamber has a long throat. A cartridge would need to be 2.950" (tip to tip) to put the amax close to the lands. He mag feeds them at 2.830", so the issue at hand is not due to screwing the pooch by a few thousandths of seating depth.

What other pressure signs were present? All of them! It blew a primer, pushed a big button, blew the ejector back into the boltface (Savage), hard bolt lift.....the works.

I would look more towards the barrel, your friend might have slight copper build in his barrel, causing massive pressure spikes. /Chris

You think this is reasonable?

 

[Niles Coyote]

Was it a Winchester primer and was the blow out on the radius of the cup where it meets the primer pocket? If so, he doesn’t have a bullet or load problem…

 

[pkt1199]

Sorry I don't have anything to add but what does "pushed a button" mean in reloading terms? I did a quick google to no avail.

 

[turbo54]

Was it a Winchester primer and was the blow out on the radius of the cup where it meets the primer pocket? If so, he doesn’t have a bullet or load problem…

They are Russian Tula primers. It wasn't the "WLR primer failure" issue where the pressure blows a hole through the primer. The primer was straight up blown out of the primer pocket.

Sorry I don't have anything to add but what does "pushed a button" mean in reloading terms? I did a quick google to no avail.

It is when (over)pressure causes the casehead to begin to flow into the ejector hole in the boltface.

A little overpressure might just leave a shiny circular spot, more pressure will cause it to actually create a high spot you can catch a fingernail on. More pressure yet will literally cause the brass to flow into the hole enough that unlocking (rotating) the bolt will shear off some of the "button", leaving a shiny raised spot you can catch a fingernail on.

Here is a picture of one from a savage:



The button from a savage is smaller in diameter than a Remington, because the ejector pin diameter of a remington is bigger. A remington's button will actually be a 1/2 moon shape. Winchester's don't have a pin-style ejector...rather, they have a notch in the bolt face, so the "button" will look like a square on them.

Hope that helps.

EDIT TO ADD: You can also get these from wet ammo. Pushing a button on wet/lubricated ammo *IS NOT* a sign of overpressure. It only means the case wasn't able to grip the chamber walls, and the case slammed rearward against the bolt. Still not a "good" thing, but not indicative that chamber pressures were too high.

 

[EddieNFL]

Never measured an AMAX, but some boat tails (SMKs) will measure 0.0005" larger at the abatement.

 

[ksthomas]

Turbo54,

there's a standard tolerance range of as much as .0005" for the SMKs (as in, .3080"-.3085" all within normal production tolerance), and I imagine the Horandy's are something pretty similar. Not the cause of the problem here.

 

[turbo54]

Turbo54,

there's a standard tolerance range of as much as .0005" for the SMKs (as in, .3080"-.3085" all within normal production tolerance), and I imagine the Horandy's are something pretty similar. Not the cause of the problem here.

'nuff said.

Thank you.