Brass will only tolerate so much movement, it doesn't matter which direction. Brass work hardens with every shot/sizing cycle. Annealing can help with this, but many if not most who aneal aren't doing themselves much good.My last two sets of Forster dies have narrowed the case at the shoulder quite a bit, from fired dimensions, .005”. This is significantly more than my Redding body dies do. I’m wondering if that might have the same effect as pushing the shoulder back too much.
In my experience, an average case will tolerate about .020 of movement. Meaning that if you move the shoulder .002 you will see a failure in the body of the case somewhere around the 10th firing if your primer pockets hold up that long.
If you move the shoulder .050 you'll likely see a failure around the 4th firing.
Some people who Neck size, and only FL size every 3rd or 4th with medium loads are getting upwards of 20 shots, I've never seen anything close to that.
In most cases (pun intended) I'm happy with 8 firings.