LMT 5.56 Carbine Action Spring AR-15 AR15
Made in USA. 17-7 PH stainless steel is a precipitation hardened stainless steel that provides high strength and hardness, excellent fatigue properties, good corrosion resistance, good formability, and minimum distortion upon heat treatment.The alloy provides valuable property combinations particularly well suited for aerospace applications. This special alloy also provides benefits for other applications requiring high strength and good corrosion resistance.
M4 spring in MIL-STD 17-7 is a corrected % of Minimum tensile strength (MTS) of 26.1. Bringing it to CS, and it changes to 27.2, which is slightly worse. Carbine works in commercial or milspec carbine receiver extension tubes. Conventional wisdom says that a USGI spring is only good for about 5k cycles.
In conclusion, PH stainless steel is more corrosion resistant and possesses slightly better strength than most chrome silicon spring.