A plunger catch is a part in a blaster. It is meant to catch onto the plunger once the blaster is primed. When the trigger is pulled, the catch moves upwards, which causes the plunger to snap back into its original position.
De-priming is the complete opposite of priming the blaster, and it involves the plunger catch. When a blaster has been primed, and if one wishes to store the blaster without the plunger ruining itself, one should de-prime the blaster. There are multiple ways of de-priming certain blasters.
To de-prime a slide blaster, pull the slide back. The slide should move freely back when the blaster has been primed and readied. Pull the slide back, and pull the trigger at the same time, and slowly move the slide back to its original position.
To de-prime a blaster like this, hold the end of the priming bar, which is usually a ring. Pull the trigger and slowly move the priming bar back to its original position. In the case of the Lock 'n Load, hold the top slide and pull the trigger. Slowly move the slide back to its original position and when the sight slams down onto the slide.
Pump the blaster and let the air leak out of the barrels overnight. This should successfully de-prime an air blaster without letting the air tank get ruined.