Springs

Springs are how power upgrades happen on airsoft rifles. A stronger spring compresses harder, pushing the piston with more force, producing higher chamber pressure, producing higher BB velocity (FPS). The math is roughly: spring rating, M-grade, scales linearly with output. An M120 spring is roughly 20% more powerful than an M100 spring. So spring choice has to track exactly to the FPS limit your site uses — usually 350 FPS for AEGs.

M-rating is the spring naming convention. Higher M-numbers = stronger springs. M90 springs produce roughly 280-290 FPS in a stock AEG cylinder — safe for any UK site, low joule. M100 produces 300-320 FPS — the common factory spring on entry AEGs. M110/M120 is the typical "slightly upgraded" range — pushing toward but under the 350 FPS site cap. M130/M140 is DMR territory — matches the higher 450 FPS DMR caps. M150+ is sniper-only — matches 500 FPS bolt-action caps. The exact FPS-per-M-grade depends on your cylinder, piston, and barrel, so always chronograph before site arrival.

Construction quality. Hardened steel springs are the standard — long service life, consistent FPS output. Irregular-pitch (IP) springs have variable spacing along the coil, which reduces "spring creep" (FPS climbing or dropping as the spring settles over the first 100 shots) and reduces noise. Anti-creep designs are similar. Brand-wise, Lonex, SHS, PDI, Modify, and Prometheus all stock airsoft-specific spring ranges with consistent M-grading. For the rest of the gearbox components that need to handle the spring load, see pistons, gears, and motors.