3 available! The Redline SR-E Lightning is a Patent Pending HPA drop engine. The Lightning is not just another cylinder replacement engine. It uses only a single solenoid, has a forward biased nozzle and fires from a true closed bolt. Due to its true closed bolt design the Lightning is much more consistent in seating the BB in the bucking from shot to shot when compared to a typical open bolt HPA engine. The result is more consistent shot to shot velocity, tighter groupings and greater accuracy at range when compared to open bolt HPA engines. A unique feature of the Lightning is that it uses a mechanically sealed, dump chamber. Rather than relying on solenoid dwell to control the volume of air used to propel the BB, the Lightning fills an internal air chamber at the pressure set by the users external supply regulator. When fired, this air chamber is mechanically sealed off from the supply and the chambers contents is released down the barrel to propel the BB. This feature contributes to the Lightnings excellent shot to shot consistency, with no air wasted do to improper dwell settings. The Lightning is also super simple to set up. Since there is no poppet dwell to tune you just set your supply regulators output pressure to match the Joules required and you are good to go. The proper amount of air needed for each shot regardless of BB weight, barrel length or any other factor is all that is released. The FCU is programmable for: 1 : Nozzle Dwell. 2: Semi Auto Max Rate of Fire 3: Full Auto / Burst Mode 4: Full Auto Rate of Fire 5: Anti Stiction Pulse 6: Selector position You can also convert the Lightning from electro-pneumatic to a mechanical-pneumatic operation with an optional conversion kit. SR-E Lightning key features: True closed bolt, single solenoid HPA cylinder replacement. Super easy to setup. Most people can just install and play with no FCU tuning needed. Easy hop tuning do to its true closed bolt design. Fixed area dump chamber design. Convertible from Electro-Pneumatic to fully Mechanical-Pneumatic with optional conversion kit. Less "joule creep" than typical HPA engines. Made in the USA