Blew a Primer _ Analysis

[Pdvdh]

I blew a primer today (1/15/2018) in my 30/375 S.I. This is a cartridge designed by elkaholic. It's been a decade or longer since I've ejected a reloaded casing with no primer.

Was using Reloder 26 in my 30/375 SI. It was the lowest powder charge of the 4 loads I had planned to shoot while conducting an abbreviated ladder test, measuring MV with a LabRadar. It was the only load I fired after the wisp of smoke and blown primer. By blown primer, I mean when the fired case was removed from the chamber, the primer was missing. The primer was intact, but laying on top of the magazine follower.

Haven't investigated causes yet, but will pull bullets and reweigh charges on the 3 remaining, unfired cartridges. A mystery. Primer pocket swelled about 0.005" - 0.006". Hoping to be able to sort out the cause...

 

[Pdvdh]

Follow-up information, after additional inspection and analysis.

On December 17, 2017, I fired a new load (bullet and powder) in my 30/375 S.I. This cartridge is a Rich Sherman (user name elkaholic) improved cartridge design. The 375 Ruger is the parent case. The case is blown out with a 40 degree shoulder, and necked down to .308 caliber.

Components and load specifics of the 12/17/2017 testing are:

Casing: Hornady 375 Ruger
Primer: Federal GM215M
Powder: 77.0gr Alliant Reloder 26
Bullet: 196.5 grain Badlands Precision - 0.010" jump until rifling contact
LabRadar MV: 3192fps
Ambient Temperature: 30F
Consequence: I only fired one round because the casing web OD just forward of the rim expanded 0.0026" with this single firing. This load was over maximum pressure for the Hornady casing, based on that measured case web expansion. The primer remained in the primer pocket. No gases escaped the case head.
________________________________
On January 15, 2018, I tested MV with a lower powder charge.
All the above component and load specifics remained the same, except a different Hornady casing was used, and the powder charge was reduced.
The temperature was 5F colder than on December 17, 2017.

Casing: Hornady 375 Ruger
Powder: 73.8gr Alliant Reloder 26
Temperature: 25F
LabRadar MV: 3101fps
Consequence: A tiny wisp of smoke was noted. Upon removing the casing from the chamber, the primer was missing. The gas/smoke escaped the perimeter of the primer. I found the primer on the top of the magazine follower. The ID of the primer pocket measures 0.215", which is 0.006" - 0.007" greater than the ID of a new unfired Hornady case primer pocket. The OD of the fired Federal primer measures ~0.211". This cartridge which was charged with 3.2gr less Reloder 26 produced 91fps less MV.

The 1/15/2018 Hornady case was exposed to less pressure, producing less MV; all consistent with a powder charge 3.2gr less than the cartridge fired on 12/17/2017. Higher pressure and higher MV was produced in the 12/17/2017 case, yet it held its primer and no gas escaped the primer pocket.
The 1/15/2018 Hornady case web and primer pocket swelled ~twice as much as the 12/17/2017 case, resulting in the release of gas against the bolt face; even though the 1/15/2018 case was loaded with 3.2gr less Reloder 26.
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Conclusion: The 1/15/2018 Hornady case head was 'softer', with a lower elastic yield strength than the 12/17/2017 Hornady case head. I'm unable to reach any other conclusion.

Further information: I had prepped four shells for an abbreviated ladder test with the LabRadar. The case that blew the primer was the lowest powder charge, and the only cartridge fired. Next day I pulled a bullet on the cartridge with the next higher charge of powder, and weighed the powder charge. Case was marked 74.6gr powder. Re-weighed the powder charge at 74.6gr. Spot on. Confirmed the powder looked exactly like Reloder 26. High confidence the 73.8gr case was correctly loaded with 73.8gr. Also, the lowered MV is consistent with the lesser powder charge, compared to the 12/17/2017 cartridge.

 

[RockyMtnMT]

Is this your first attemp with rl-26 in this combo?

Steve

 

[Pdvdh]

Yes these were my first two efforts. My only two field-fire outings with this bullet and powder in my 30/375 S.I. - 12/17/2017 and 1/15/2018.

I'd never loaded and fired Reloder 26 in any cartridge prior to 12/17/2017. I'd never loaded and shot this Badlands Precision bullet prior to 12/17/2017. Only one shot fired on each date in the 30/375 S.I. The 12/17/2017 load exceeded a maximum case pressure for the Hornady casing. I'm not certain the pressure on 1/15/2018 was excessive. It's possible the pressure was acceptable, but that this different Hornady case head was defective/soft. A lower strain yield.

I looked down into the Hornady casing with the blown primer with a flash light. Didn't see any obvious dimensional flaws inside the casing. Wasn't disfigured internally. I'd already weighed all 50 of the Hornady cases that came in the box before I ever loaded any of them, and there were no extreme outliers based on casing weights. Nothing to indicate a very light case with less brass.

 

[RockyMtnMT]

From my perch a thousand miles or so away, you are the victim of bad brass. I would contiue on with load development.

Steve

 

[Pdvdh]

From my perch a thousand miles or so away, you are the victim of bad brass. I would continue on with load development.

Steve

Appreciate your thoughts Steve. I don't think I've overlooked anything that points to operator error, or another (better) explanation. But it's generally good to receive and consider others' thoughts.

A secondary interesting observation in the process of examining the bolt head: This is a BAT Machine Company HR action. The action body and bolt were salt bath nitride treated by BAT Machine company. I've seen bolt faces following blown primers on other bolt heads that were not nitrided in the past and normally there's a slight, yet noticable erosion pattern on the face of the bolt face - in a circular pattern matching the diameter of the primer pocket. The escaped gas torches and etches the bolt face. The nitride treatment coating seems to have helped protect this bolt face from that erosion. Look's smooth to me. I'll have to scratch the surface with a needle and feel for an eroded surface. I do see the ring where the gas hit the bolt face, but I do not see any erosion into the bolt face.

 

[Edd]

That is too much velocity for a case that size and a 200 grain bullet. You need more Pixie Dust.

 

[tbrice23]

Phorwath, is this barrel nitrided?

 

[Pdvdh]

That is too much velocity for a case that size and a 200 grain bullet. You need more Pixie Dust.

I think elkaholic would disagree. He's fired the 215 Berger from his 30/375 at MV exceeding 3,200fps. But he's comfortable shooting them at 3,100fps. If he blew a primer, he never mentioned it to me.

 

[Edd]

I think elkaholic would disagree.....

Of course he would. I'm hoping he doesn't get himself or someone hurt.

 

[Pdvdh]

Phorwath, is this barrel nitrided?

Yes, but it provides good accuracy and has been a reliable performer so far. If it's on the same death march as your nitrided McGowan barrel, this would be the very first indication.

elkaholic's barrel is also nitrided by the same salt bath nitride treatment company. He's got more than 1,000 rounds on his nitrided barrel and it's maintaining excellent accuracy. His rifle maintains its tack driving precision.

I can't say my barrel will not suffer a post-nitride treatment death march. But it's been performing fine with RL33 and 215 Bergers and 225 Hornady ELD-Ms up until now. Nothing of concern so far.

 

[tbrice23]

Ok.

Hopefully it is just soft brass.

 

[Barrelnut]

Is this the first time for copper bullets?

 

[Pdvdh]

Of course he would. I'm hoping he doesn't get himself or someone hurt.

You should bring that to elkaholic's attention, if you haven't yet done so. The 'conversation' feature is available if that weighs heavily on your mind.

Beyond that, do you have anything helpful toward explaining why a casing with lower pressure (confirmed by lower MV) blows a primer and the case head expands more than twice the amount of the higher pressure/higher MV cartridge case?

Even if I give you the benefit of the doubt that you're 100% correct that I'm red-lining the cartridge pressure... Anything else to offer to explain the additional case head expansion on the lower pressured cartridge case?