I got this today at the range. This was shot in my CZ550 in .375 H&H. The brass was new Remington that I bought a couple of years ago. The bullets were 300 grain TSXs. The failure on the left occurred with 74 grains of Win 748. The one on the right occurred with 75 grains of Win 748. Both shots were fliers. There were no pressure signs, and none of the other brass fired today showed any issue. No one there had seen anything like this before.

When I prepped the brass it seemed a little hard to chamfer and deburr. Didn't want to trim smoothly.

Anyone have any idea what caused this? I'm tempted to toss the whole lot.

LWD

What is you neck brass thickness?

I have seen this before, with and without the chip. I figured it was caused by a metal fold during forming somehow.

I have had cases come out my 303 looking like this. my cases that failed like this were stood on, so the necks were bent closed. I got them resized and they looked fine, i marked the squashed ones to keep track of what happens to them, they all broke in a very similar fasion to yours. I will post pictures of mine tonight.
and NO, i wont try that again!

That's weird and worrisome; I would throw away the whole lot. Did you find the missing neck chips?

I had some similar case failures years ago. I took the rest of that bag of new brass and annealed the necks and had no further problems with the rest of those cases. I figured the manufacturer had just screwed up the final cases annealling.

Anneal the necks.

i've seen this happen before. the cause was in the bullet seating. the base of the bullet caught up on the edge of the case mouth and sort of folded a tear in the mouth, then when fired the brass blew out where it was damaged. anealing and chamfering fixed the problem

Thank you all for your replies.

Brass thickness on these two failures measured .0125 to .0135. I measured the thickness on some PMC and got .0135 to .018

I did not find the chips anywhere. I assume they went downrange a bit.

The chamfering on these casemouths is rather rough, so I would not be surprised if what Butchloc suggests is the case---the bullet seating caught something.

Thanks again,

LWD

That dark coloration at the case mouth indicates that enough pressure wasn't generated to sufficiently expand the case to seal the gasses in to the chamber, thereby causing a blowback kind of situation where gasses get past the mouth. It could be caused by a light load, but in this case it very well may be the brass was so brittle that it didn't generate enough pressure to expand that particular brass. I know you said it was new brass, but did you by chance use any kind of polishing media on the brass with ammonia in it?

I also see you have had it a couple of years. Where did you have it stored? That may have had some effect on the metalurgy of the brass also.

33806, thanks for the input. These were shot with max and 1 grain under max loads so there sure should have been enough pressure. I did not use any cleaner of any sort on them, and they have been in the garage in a cardboard box.

I'm tossing the whole lot.

LWD