HPA (High Pressure Air)

A remote tank — usually the same paintball tanks used in that sport — supplies air at high pressure to a regulator, which drops it to a set output pressure. A solenoid valve opens for a precisely timed burst on each shot, so an HPA engine can hit exact FPS numbers and rate-of-fire settings a mechanical gearbox only approximates.

The trade-offs are a hose running to an external tank, a fill station or dedicated tank refills, and a control board that adds electronics most other platforms don't have. In return, HPA gives programmable pre-cocking, burst modes and consistency that make it common in speedsoft and DMR builds where shot-to-shot repeatability matters most.

Because output is set electronically rather than by physical parts, two players can share one gun's "engine" settings by simply copying regulator pressure and control-board profile, which is unusually easy compared to matching mechanical spring and gearbox tunes.