How do I prevent this? Weigh my bullets before shooting?
My guess is the best countermeasure would be to buy good quality ammo. I've heard of some rimfire benchrest guys who weigh the rounds, even the match grade stuff. But they are looking for consistency, not reliability. I haven't tried weighing them, but for bulk packed rounds I would guess the variation in the weight of the bullet would make it tough to find a powder charge that was off by a couple tenths of a grain.