From what you said about your annealing safeguards, that is not the problem. My question is did you Anneal because you were seeing spring back from sizing or just hoping to extend Brass life? The fact that you only got 4 rounds to chamber in a box is a cause for concern to me. Were these hot loads? How are you bumping the shoulder? Are you using a shoulder set comparator for assessing sized headspace and setback and potential spring back after running through a sizing or using a chamber test (i.e. Does or does not chamber..). Also are you trimming cases as per your prep? I have one bolt gun that I have to be very diligent with case length or I get I inconsistent chamberings (regardless of how many thou's I set the shoulder back). Length, shoulder setback, or COAL most likely the culprit.
Annealing is (generally but not always) a good practice if done correctly. I track my loads after annealing and have found that with most of my bolt guns shoot the toughest groups the 3rd reload after annealing. Remember, because your Load development most likely happened under a condition where your Brass was/is partially work hardened, unless you check neck thickness you will most likely have variability in neck tension amongst your rounds...especially directly after annealing where the Brass is more mallable and has less "memory/spring back" from being work hardened. If you do anneal, depending on the die used, either go to a carbide expander ball (redding) or polish the expander ball to prevent pulling the shoulder up upon dragging the ball back through annealed Brass.
Last question, are you FL Sizing/using bushing die to set shoulder back, or sizing for a single gun and neck sizing or using a body die the. Following with a collet die to reduce runout?
Annealing is (generally but not always) a good practice if done correctly. I track my loads after annealing and have found that with most of my bolt guns shoot the toughest groups the 3rd reload after annealing. Remember, because your Load development most likely happened under a condition where your Brass was/is partially work hardened, unless you check neck thickness you will most likely have variability in neck tension amongst your rounds...especially directly after annealing where the Brass is more mallable and has less "memory/spring back" from being work hardened. If you do anneal, depending on the die used, either go to a carbide expander ball (redding) or polish the expander ball to prevent pulling the shoulder up upon dragging the ball back through annealed Brass.
Last question, are you FL Sizing/using bushing die to set shoulder back, or sizing for a single gun and neck sizing or using a body die the. Following with a collet die to reduce runout?