Jumbo Acoustic Sealant Applicator Gun
Retract the plunger by pressing the thumb plate and pulling the plunger back as far as it will go. Feed the nozzle of the cartridge through the hole at the end of the gun so that the cartridge fits into the collar. Then press the trigger and repeat until the plunger enters the hollow at the rear of the cartridge.
The sprung trigger is used to feed the plunger down the gun and apply pressure to the cartridge, thus pushing the sealant through the nozzle. To release the pressure you need only press the thumb plate and pull back on the plunger!