Friend fired 60 cases of new factory Winchester 223 from TC Contender rifle.

De-primed and sized, then noticed during trimming that 7 of the 60 had neck splits.

During trimming and deburring, noticed metal seemed harder.

Also noted primers seated much easier than normal.

Anybody else ever noted split necks and loose pockets on once fired brass factory brass ?

Thanks for your help !

Had a bunch of Split Necks on some Remington factory 22 Hornet ammo back in the early `70s. They replaced them at 4 boxes for the 2 I sent back to them.

Apparently the ones I had, had been on the shelf of a hardware store for many years before I got them. Or, perhaps the Annealing was hosed-up.

Best of luck to you.

Hot rounds will loosen pockets. Loose chamber could cause necks to stretch. Could be some bad brass mixed in to the batch.