If you smoked a fireformed case and set up your FL die to just bump the shoulder I don't know.....
You been keeping your chamber clean, cleaning only from the breech?
Maybe try loading to a longer OAL. Seat a bullet into an empty case way long, smoke it black, then try to chamber it. Note the marks on the bullet. Seat the bullet a little deeper, and repeat until it chambers. Set it back .010-.020 after it chambers and check your OAL. Is it longer than factory? Will it fit in your mag? Try loading this way, it may lower operating pressure
(and it might not.) and as a side benefit, maybe improve your accuracy.
Case head failures are nothing to laugh at. They're REALLY not funny in magazine fed autoloaders
Maybe you got a batch of bad brass?
I'm not just a gun.
I'm YOUR gun.