M1 Case Splits

[SoCal1911]

A few reloads with case splits from M1 from CMP.
1969 Lake City 30-06, 3 time fired. Load 46Grs 4895, 150Gr FMJ, Winchester primer, brass was trimmed. 5 of 40 rounds fired split. See attached picture, splits are above the the blue mark (necks buffed to show splits). I have seen (in other rifles) neck splits at the mouth, and case separations but not were these splits are located. From what I have researched that this brass should last at least 5x reloads.
What is the reason why the cases are splitting?
Should I scrap the whole batch of this brass?
Still have 100 plus loaded and concerned if they should be pulled and the brass scrapped.

What are your thoughts?

[jsanch03]

[pacrat]

Appears to be fatigue cracks due to brittle necks.

Consider that there is no "One Right Answer". To many variables involved for such.

Every lot of brass is different. Every rifle chamber is different. Every sizing die is different.

Your issue is fairly common when the stars fail to align. Can be mitigated to some extent by annealing your cases.

[tabascoz28]

Could be a bad batch, could need annealing after every firing.

[JackEllis]

I've had the same thing happen with some used .243 cases AFTER I reloaded and fired them. The ones I was just able to find were a mix of Remington and Federal. Not sure how many times they were reloaded before I got them. I only scrap cases that show signs of splits or head separation.

I'm now using a batch of cases that were purportedly once-fired when I bought them. It'll take a few years to find out how many times I can reload them.

[divingin]

Measure a loaded round vs a fired case for outside neck diameter. If the difference is less than 3 or 4 thousandths, your problem is likely brittle brass. If it's more, it would be a combination of brittle(ish) brass and a generous chamber.

50 year old brass may well have been affected by storage conditions (and there is some evidence that brass ages just sitting; not sure if that's fact or not, but I do believe it.) If it has hardened, for whatever reason, it will split much more readily than newer, unworked brass.

If you can anneal the rest of it, it may or may not help, but also wouldn't hurt anything.