Airsoft pellets are designed to provide durable ammunition for airsoft guns. They should never be reused as projectiles for use in a BB gun, as they can cause irreparable damage to your weapon. Airsoft pellets are subjected to stress the moment they’re fired, therefore they’re more likely to crack or shatter when reused, which can cause serious damage to your magazine.
An acceptable reuse method is using old pellets in airsoft mines or booby traps. For example, the M18A1 spring loaded mine is an ideal choice for airsoft pellet reuse as it launches pellets outwards when triggered.