27.4gr of 8208 should be plenty safe with a 123gr A-max in Hornady brass.
Visually inspect your chamber and bore, and closely check your bolt and extractor for cracks (especially if you haven't tried factory ammo since using the potentially hot reloads with 28.4gr of 8208). A bolt doesn't necessarily become completely inoperative all at once.
It might indeed be a mechanical problem and not a reloading issue.
Visually inspect your chamber and bore, and closely check your bolt and extractor for cracks (especially if you haven't tried factory ammo since using the potentially hot reloads with 28.4gr of 8208). A bolt doesn't necessarily become completely inoperative all at once.
It might indeed be a mechanical problem and not a reloading issue.
Drifter