What caused this???

[Halleywood]

I doing some load development in my 7mm STW with new Remington brass this morning and 2 of the 24 rounds fired had this happen to the case. I've never seen or heard of brass caving inward.

My only thought is because it's new brass the shoulders were bumped a good 7 to 10 thousandths more than my fired cases measure. Could that shoulder bump cause gas to escape backwards and cave the brass?

Should I throw them away? I was scared to shoot again after the first one but there was nothing in my chamber that would have caused it.

 

[lightflight]

Case lube dent?

 

[Halleywood]

No. The dent happened when I fired the round. I'm 100% sure of this as I inspected each case before loading it.

 

[Korhil78]

You said you were developing a load. What recipe was it and where did you start at on powder charge weight? Sometimes this happens when you make a load that has too light of a powder charge which can cause gas to blow back into the chamber and sent the case as you see there. Means the pressure is too low and doesn't the brass doesn't expand to seal the chamber properly.

 

[lightflight]

No. The dent happened when I fired the round. I'm 100% sure of this as I inspected each case before loading it.

good point. Plus I guess after firing a case lube dent it would push it back out.

 

[Halleywood]

You said you were developing a load. What recipe was it and where did you start at on powder charge weight? Sometimes this happens when you make a load that has too light of a powder charge which can cause gas to blow back into the chamber and sent the case as you see there. Means the pressure is too low and doesn't the brass doesn't expand to seal the chamber properly.

Thanks for the reply. The load I used is .7 grains above max load according to Berger reloading manual so I wouldn't think it would be too light of a charge. I worked up to this load with multiple times fired brass and was doing some seating testing with the same charge.

 

[Korhil78]

Well I am pretty sure that your brass is not sealing up the chamber properly and allowing gas to escape back into the chamber. Something is causing that, whether your shoulders or pushed back to far or there was something inside the chamber which caused it.

 

[Barrelnut]

Maybe a donut ring where the shoulder meets the case wall. Looks like just one small section of the shoulder was too thick to expand and seal the chamber. If you cut the case open, you maybe able to see cause.

 

[Pdvdh]

This can happen when using a light load with a slow burning powder. It's from the case not sealing to the chamber tightly and allowing high pressure gas to act on the exterior of the cartridge case.

The fact that the shoulder had 0.007" to 0.010" excessive slop (headspace) may indeed, be a contributing factor. Allowing gas to slip past the exterior of the case. However folks fireform brass casings all the time, but probably with faster burning powder than you were using.

You said you're using more than the max load of powder. Dunno what to say about that. I think it's a combination of a slow burning powder and excessive headspace. My guesstimation and information...

 

[woods]

Gas is getting between the case body and the chamber walls

Either from too light a load to seal at the neck OR a gas escaping from the case head area and trying to move forward to exit

You get the same thing with a case head separation where the gas comes out of the separation and moves forward to exit

技

 

[highridge1]

I was looking at some Berger Load data for the 338 Ultra and it was very downloaded. Their listed max was 10 grs under a safe max load....

 

[LoneTraveler]

I have seen this in 264 Win. Mag. cases. The powder was 1967 era surplus H-4831. Some case were normal and some showed the same crease as yours. He said they did not kick as the undamaged case loads did. He tore the rest of the shells down and found his scale had got bumped or sabotaged and the beam weight had got moved 20 or 30 gr. from the publicized load he wanted. I suggest dis-assembling any loads left from that session. BE SAFE. Weigh powder as it is removed from cases, Write down the weights as removed. Check Powder, Scales and Powder measure. Something may went a fowl. Good Luck

 

[MagnumManiac]

This appears a lot on the smaller RUM cases, below 375 cal, even if the powder charge is 'normal', it's most likely caused by an ignition problem where the powder doesn't 'progress' normally as it should.
I remember reading a tech article about this phenomenon from one of the big bullet manufacturers when they were working up loads for the then new 7RUM, I don't recall which manufacturer it was, but they experienced this with some start to middle loads with very slow burning powders.
The only time I've seen this was in a custom 25WSM, it did this in the same circumstances.

Anything like this should be seen as a warning to ignition problems and also that this could lead to an excessive pressure situation because the burn may be starting and then stopping not sealing the chamber.

Cheers.
gun)

 

[Lefty7mmstw]

What was your load??
I've only seen this with mild doses of slow burning powders if the pressure is too low or a big case with a light bullet load and a mild dose of powder that is rather fast for the case. The last time I had it was last winter burning up some 125 bt's in my 300win with 4895; gotta shoot what ya got these days and the 125's were gathering dust.