SS AIRSOFT Custom Built HPA airsoft rifle. We build some of the best custom HPA airsoft replicas you will find on the market. All weapons are test fired ,tuned and adjusted to work perfectly right out of the box. This item has been custom installed here at SS Airsoft.  Includes, Gun, and Polarstar Jack SS Custom HPA Build Blue ARP-556 2.0  G&G Airsoft ARP-556 2.0 Black Archwick 60 Degree NBR Rubber Airsoft AEG Hop-Up Bucking PolarStar Airsoft JACK Electro-Pneumatic Gearbox Conversion Kit V2 Fire Modes: Semi/Full-Auto, Safety Battery:Sold Separately  7.4V mini lipo battery with jst connector Hopup: Yes, Adjustable Package Includes: Gun, Magazine, Manual Manufacturer: G&G FPS Range: 330-400 The JACK™ system was designed to answer the demand for an affordable, high performance HPA conversion for AEG's. The system is a drop-in cylinder replacement that is universally compatible with a wide range of gearbox versions that have center-line nozzles. Similar to its sister product, the F1, it replaces the original gearbox components with a programmable pneumatic system allowing for higher performance and greater reliability over a gear driven system. Although economically priced, JACK™ still retains the same performance and quality you have come to expect from PolarStar products. SPECS Velocity: 500FPS w/ .20g @ 120psi. The Jack allows for easy velocity adjustment. Using a standard V2 as an example, velocity can be adjusted from below 100fps and up to approximately 500fps with a .20g BB. Longer barrels will increase the maximum FPS while shorter barrels will decrease it. ROF: 30RPS+ The maximum cyclic rate of the Jack is affected by several factors, however, 30 rounds per second is a conservative number. Most configurations will exceed this easily. Air Efficiency: 1200 shots from 13/3000 @ 1.5J (80PSI w/ .28g) The JACK is extrememly efficient. The patent pending design of the F1 allows for the most direct air path to the nozzle with minimum dead volume resulting in better flow, faster response and less air used per shot. Using a stock VFC M as a test platform, the JACK was able to fire approximately 1200 rounds for a 13ci/3000psi cylinder before pressure dropped below regulated output.