Pull the bullets and reload with known quantity of powder.
Rifle loads with quick burning shotgun powders can quickly get overpressure.
For example, 20 grains of green dot and a 125 bullet is roughly 41kpsi; 30 grains is 74kpsi (and not even a full case).
All is takes is one round out of the 300/400 to accidentally have 30 grains and you have a big problem.
