Removing the breechplug on a charged weapon is sort of like taking apart a pipe bomb.

As far as I have read, there are three, maybe less, recommended unloading procedures (short of shooting):

1. Pull the ball with worm or scree (dunno if a sabot will let go of the bullet)
2. Submerge the charge (killing it with water), then disassemble
3. C02 dischargers ?? (used to be around, but I have zero experience with them)