PolarStar Airsoft JACK Electro-Pneumatic Gearbox Conversion Kit (Model: M249)

PolarStar JACK Electro-Pneumatic Gearbox Conversion Kit — M249 Model
Precision HPA power for your AEG: faster, cleaner, and more consistent than gears.

If you’re ready to leave noisy gear trains behind and step into the world of true electro-pneumatic performance, the PolarStar JACK (M249) conversion kit is built to do exactly that. Designed and manufactured in the U.S.A., JACK is a compact, no-nonsense HPA conversion that drops into your gearbox shell and turns a compatible AEG into an instantaneously responsive, highly tunable HPA platform. The M249-specific configuration gives belt-fed operators the efficiency and reliability they need for heavy sustained fire.

Why JACK? — The advantages at a glance
• Instantaneous trigger response — JACK reacts faster than even a Li-Po-powered AEG. Pull the trigger and the shot is delivered with surgical timing.
• Superior shot consistency — CNC aluminum components, an optimized flow profile, and a high-performance Delrin nozzle deliver tight FPS spread and repeatable performance.
• Ultra simple internals — JACK has only one moving part (the nozzle/poppet), which makes it incredibly reliable, easy to maintain, and easy to service in the field.
• High and low temperature reliable — JACK is engineered to function in damp, freezing, or otherwise harsh climates without compromising performance.
• Efficient air usage — Minimal dead volume, refined flow paths, and precise dwell control mean more shots per tank compared to many competing systems.

Built for customization and control
JACK is more than a drop-in replacement — it’s a fully programmable fire control solution. The included Fire Control Unit (FCU) features an LCD and five-position joystick that let you set cyclic rate, poppet dwell, and fire modes on the fly. Choose between Semi/Full Auto, Semi Only, and Variable Burst modes to match your ruleset or mission. The FCU is compact and MOSFET-sized so it fits neatly in common battery compartments alongside a small Li-ion pack.

Performance you can tune
Velocity is adjusted by a combination of regulated input pressure and precise poppet dwell — giving you predictable, fine-increment control over FPS (for example, an M4 platform can be tuned from under 280 FPS up to roughly 500 FPS with a .20g BB). JACK’s universal cylinder design is compatible with a range of gearbox versions that use center-line nozzles, making it flexible for multiple platforms when properly set up.

Made for durability and simplicity
Assembled from CNC machined aluminum with a high-performance Delrin nozzle, JACK is intentionally minimal: six parts total and easily disassembled by hand. The nozzle serves as the poppet valve piloted by a solenoid — the same core principle used in PolarStar’s Fusion Engine — which gives JACK its distinctive, crisp muzzle report while keeping mechanical complexity to a minimum.

What you need to operate JACK (not included)
• A complete TM-spec AEG with a gearbox shell (JACK installs into the gearbox shell)
• Regulated air rig + HPA tank (never use CO₂/propane with JACK)
• Small Li-ion battery for the FCU (sold separately)

Safety & HPA best practices (must read)
JACK requires HPA or nitrogen only — do not use CO₂ or propane. Follow HPA safety rules: never add oil to tank fill valves, use trained professionals to refill tanks, verify regulator pressure (do not exceed 120 PSI), hydro-test tanks per manufacturer recommendations, and always transport and store tanks safely. Always shut off your tank and bleed lines after use.

Final word
PolarStar’s JACK (M249) brings HPA’s speed, consistency, and tunability into a compact, field-serviceable package that transforms how an AEG performs. If you want the crisp trigger, adjustable fire modes, and rock-steady shot-to-shot consistency of a high-end HPA system — but with minimal complexity — JACK is one of the smartest conversions you can make. Built in the USA, serviceable in seconds, and tuned on the fly, JACK is HPA made practical.