The spring is a fundamental part of the gearbox because its strength, along with the air seal, affects the overall performance of the rifle. Low-quality springs, although they often have above-average performance compared to their rated value, quickly lose their stiffness, shorten, or in extreme cases, can break (due to storing the rifle with a compressed spring or in a pre-cocked state).
From the workshop of Retro Arms, famous for their quality CNC gearboxes, comes another finely tuned upgrade part: a high-quality spring made from valve wire alloyed with silicon and chromium (SiCr) that retains its stiffness after thousands of shots and does not deform.
Progressive (variable) winding makes the compression easier in the first phase of the piston movement while not reducing the performance. The outer diameter of the spring is 14.5 mm.
The rated value of M120 corresponds to a speed of 120 m/s with an average barrel length. With a good air seal or a longer barrel, the performance will be higher.