A trigger sprayer is a mechanism which sprays a fine spray of either liquid or compressed air to the air to generate a sudden, forceful blast of air which propels the expended projectile straight into an opponent, animal, or object. The name " Trigger "sprayer" derives from its usage in military applications, where it is used to shoot an empty cartridge or rifle round directly at an attacker. Trigger type mechanisms can be either gas-powered or electric, depending on your desired spray timing and power. Gas Trigger Sprayers are typically more powerful than electrically operated Trigger Sprayers.
A close relative of the trigger sprayer is the 24-mm self-defense shotgun model, which is essentially identical to its less powerful cousin. The difference between the two is primarily the size of the internal parts. The larger internal parts of the 24mm model are capable of sustaining a high velocity firing (this is contrary to the gas-trigger mechanisms, which tend to experience poor BB feeding rates due to their lack of internal parts with sufficient length to accommodate high velocity firing). In addition to the larger internal parts, the internals of both types of models utilize similar external components to propel the BB's (which may not include a spring), including breech pins, hammer head, etc.
Both types of trigger sprayers employ external moving parts that propel and send the BB's to their target. The key difference between the two is in the "pulling" mechanism. A trigger sprayer requires a pin to be pulled down or pushed forward to start the spray; a semi-automatic 24mm trigger sprayer, on the other hand, requires the trigger to be manually pulled or pushed in order for the mechanism to engage. Pulling the pin requires more physical effort than pushing the trigger. The result is that in a semi-automatic 24mm trigger sprayer, the sprays are expelled at a much faster rate than their gas trigger counterparts.
In summary, there are three main differences between the various types of trigger systems for the various models available. First, the size of the trigger itself will determine how effective the trigger is. Secondly, both types of trigger can propel BB's in a straight line or in an arc pattern, depending upon which direction the trigger is pushed. Lastly, both types of trigger can have different exit points, either at the front end of the gun (the semi-automatic) or at the back end (the fully automatic). Note that the term "receiver" refers to the part of the gun that holds the BB when it exits the gun in an arc pattern.