Blew out a Primer and expanded the pocket.

[gmcttr]

I've been reloading since the '70s but am new to 300 BLK.

I had worked up loads for a 130gr OTFB Pulled bullet (from American Reloading) and H110 using Hodgdon data which lists a "starting load" @ 17.1grs with a "maximum load" @18.6grs. The brass was new Starline.

Starting with the "starting load" all went as expected until the second shot with 18.5grs of H110 when the primer popped out (velocity was as expected from the loading data). I fired the remaining 8 rounds without incident.

All charges were thrown and weighed to within +/- 0.02grs with extra care as I was working up the load.

No problem since I had found the most accurate loading was lower at 18.3grs.

What surprised me was that the primer pocket expanded to the point that a new primer justs falls in and out of the pocket. That's a new one to me. Anyone else have a pocket diameter expanded or have any thoughts on why this would happen on a single round with no obvious signs of overpressure on the other 9 rounds of the same load?

 

[oldpink]

That's classic overpressure load symptom right there, but it's hard to see how it went that way when you weighed your charge and used the starting load.
All the rest of your loads went as expected, so something else (can't figure out what) happened with that one load.

 

[oldpink]

I know this is probably a longshot, given your long experience with reloading, but thinking about it, is it possible that the load in question somehow had its bullet somehow jam into the rifling or slide rearward into the case?
Either condition can raise pressures quite a bit.
Your charge weight is as consistent as could be gotten, and (assuming) that you're using all the same brass (no mixed headstamps, especially military), it's impossible to think offhand exactly what else could have done that.

 

[BiscuitsandGravy]

I've loaded quite a few 300's with that recipe and haven't seen any pressure issues. Using LC brass. Could it be as simple as a defective fresh case?

Curious if you clean the American Reloading 130's?

 

[gmcttr]

That's classic overpressure load symptom right there...

So permanently expanding the primer pocket is typical with a blown out primer? With .223's in a AR and 22-250's in a bolt gun, I've seen severely flattened primers, with too high of pressures, but have never lost a primer/had the pocket expand.

...is it possible that the load in question somehow had its bullet somehow jam into the rifling or slide rearward into the case?...

...and (assuming) that you're using all the same brass (no mixed headstamps, especially military)...

All brass was new Starline which I sized. While nothing is impossible, I used a Lee Factory Crimp die (collet type) to crimp in the bullet's cannelure and I did not notice any feeding issues. With the bullet's profile there would have been lots of space between it and the rifling (as loaded). Finished rounds were randomly checked with a Sheridan Engineering Ammunition Gauge.

I've loaded quite a few 300's with that recipe and haven't seen any pressure issues. Using LC brass. Could it be as simple as a defective fresh case?

Curious if you clean the American Reloading 130's?

Defective case...again, anything is possible, but the pockets felt uniform while hand seating the primers and measurements after firing show the neck wall thickness, interior depth from rim to base web and case length matches the rest of the batch.

Here's a link to the bullets used...https://americanreloading.com/en/30-caliber-308/930-308-130gr-sierra-otfb-pulled-250ct.html

I did not batch clean the pulled bullets but did use alcohol to clean a couple that had a light black residue on them (sealer?). Each one was visually inspected with one being rejected due to a large nick. The only defect I would not have noticed is if one had been slightly out of round/oval.

Thanks for the questions. I expect this one to remain 'one of those things'. I was mostly curious if the permanently expanded pocket typically went along with a blown primer.

FWIW...my best group with H110 came with 18.3 grs and the groups opened up considerably with the 18.5 grs load in question even though the StdDev. and Spread was better.

 

[OHOIAN]

I would suspect the pulled bullets. One may have been different somehow.

 

[gmcttr]

You do have to look out for the occasional different bullet mixed in, although I'm sure that didn't happen this time. In the future I will stay farther below suggested max loads with the pulled bullets in case of damage that can't be easily seen.

 

[oldpink]

It doesn't happen every time that pressure levels get high, but what I have read says that primer pockets can indeed get stretched, and my single experience with over-pressure loads had had that happen.

 

[BiscuitsandGravy]

Do you sort the pulled bullets from American Reloading?

Each batch we've purchased is not 100% consistently the same. We hand sort with a digital scale and usually end up with some 120's, 115's, etc.

Just a fyi..

 

[gmcttr]

I did not weigh this batch as I thought it was a rather distinctive bullet with it's deep cannelure. If there were another weight of the same design mixed in that only weighed 5 grs +/-, I might have missed it. I will weigh a large sample and see if i find any variation.

On a side note, after receiving an order of 500 "mixed" 168/175 grs SMK's, I weighed them all and there were only 13 of the 168's.....a lot of weighing...lol.

Edit: I weighed the remaining 150 bullets and they were all the correct 130 grs. flat base except for the one obvious 220 gr SMK. Of course that doesn't mean the fired bullets were all the same. The round that blew out the primer was 10-29 fps faster than the other 9 of that loading so I doubt a 'heavy' bullet would have been the cause.

 

[jhart]

One thing that pops to mind but its a long shot. What about internal volume of the case. Maybe it was a manufacturing defect such that side walls were slightly thicker or not as deep.

 

[gmcttr]

One thing that pops to mind but its a long shot. What about internal volume of the case. Maybe it was a manufacturing defect such that side walls were slightly thicker or not as deep.

From post #5...

...Defective case...again, anything is possible, but the pockets felt uniform while hand seating the primers and measurements after firing show the neck wall thickness, interior depth from rim to base web and case length matches the rest of the batch....

After reading your post I checked the volume as best as I could by filling the bad case and another from the same batch with water and they both held 1.5cc's

 

[oldpink]

Okay, I give up.
Gremlins?

 

[gmcttr]

Okay, I give up.
Gremlins?

Yep...

On the bright side, I got 200, 300 Blackout cases made from .223 brass today.

 

[oldpink]

Yep...

On the bright side, I got 200, 300 Blackout cases made from .223 brass today.

It's a real mystery, that's for sure, but at least you have been productive with your case-forming operation.