There is no compressed air in a blaster. It would need something to hold compressed air and a mechanism to release it. The piston pushes the amount of air in the cylinder through the nozzle and the gel moves down the barrel with the flow of air
Like those little electric fans (so called compressors) you put on a car intake… supposedly an electric ‘supercharger’. They are not a compressor as they don’t compress the air, they are a fan that moves the air
A gel blaster and a pea shooter use the flow of air provided by lungs or the piston or cylinder/piston… the only time a cylinder on a blaster compresses air is if you put your finger over the end and push the plunger towards the nozzle (like testing a seal) … a gel ball is incapable of blocking the end of the nozzle (like a finger)… the increased pressure from the flow of the air from the cylinder moves the gel easily at the same velocity as the air flow…as long as the gel ball is the correct size for the id of the barrel… too big for the barrel, the gel will break, too small, it will be overtaken by the airflow and dribble out of the barrel.
A gel blaster and gel ball is not unlike you and a water slide… the gel ball is introduced into the barrel via the T piece like a person getting into the ‘breech’ of a waterslide (although the water is already running)… the blaster piston comes forward and pushes the gel… the person drops into the flow of the water…the gel goes with the air flow, the person goes with the water flow the gel flies out of the barrel and the air dissipates… the person flies out of the end of the waterslide and the water goes back in the pool.
It is flow, no compressing