After installing this spring and:
- Guarder aluminum piston head w/ bearing
- CA polycarb piston
- CA super torque-up gears
- CA anti-reversal latch
- JBU 6.03x550mm inner barrel
- King Arms one piece metal hop up unit
- Systema hop-up bucking
* Echo 1 black H-type hopup spacer
Into an otherwise stock A&K SR-25, the rifle was chrono'd at 400-405fps w/ .40g Madbull BB. Mathematically, that equates to about 565fps w/ .2g. This was with a near-ideal air seal.
For comparison, with the same gearbox/rifle setup and a Guarder SP140 spring, the rifle chronographed at 500fps with a .2g BB.
- Very high velocity (over 550fps with the right air seal)
- Very little deformation after 1,000 rounds and six months in a gearbox (swapped for an SP140 for velocity regulations)
- Makes gearbox disassembly/reassembly difficult, if not dangerous. Use a bolt or an M4 T6/LE stock retention screw (threaded into the spring guide) to make those processes easier.