AEG Progressive Spring by ASG ULTIMATE

The spring is a key component of the gearbox as its strength—combined with air seal quality—determines the gun's overall performance. Low-quality springs may offer higher-than-rated output at first, but quickly lose tension, shorten, or even break—especially when stored compressed or used with pre-cocking systems.
The ULTIMATE upgrade spring from ASG is engineered for maximum consistency and durability. Manufactured from high-quality SiCr spring steel (silicon-chrome), it meets military specs and withstands wear, even under high rates of fire.
The progressive winding design starts softer and builds up, reducing stress on the gearbox and motor. Both ends are closed and ground for stability and a secure fit. Each spring is factory pre-tensioned to minimize initial power drop. The black zinc coating protects against corrosion without affecting performance.

Installation

When installing a progressive spring, the tighter-wound end (with denser coils) goes onto the spring guide. The colored-marked end by ASG ULTIMATE goes into the piston.

ULTIMATE Spring Ratings and Dimensions Table

Key Features

• Military-grade SiCr spring steel – high strength and durability.
• Progressive winding – reduces firing stress, gearbox-friendly.
• Closed and ground ends – improve alignment and spring stability.
• Factory pre-tensioned – stable power without break-in drop.
• Black zinc coating – corrosion resistance without friction loss.
• Color-coded stiffness – quick and easy identification.

Technical Specifications

• Rating: M135
• Estimated output after installation: approx. 135 m/s (tested with 6.03 mm – 300 mm barrel)
• Material: SiCr spring steel
• Finish: Black zinc coating
• Winding: Progressive
• Compatibility: Most AEG gearboxes (except V2.5, L85, PSG-1, and other atypical types)

Package Contents

• 1× ASG ULTIMATE AEG Spring