The Spring M105 for AEG from Ultimate (ASG) is a performance upgrade spring designed for AEG gearbox systems, offering a balanced increase in power output while maintaining reliable cycling and long-term durability.

Manufactured from high-quality SiCr (silicon-chromium) spring steel, this spring is engineered for consistent tension, reduced deformation over time, and stable performance under repeated compression. The design typically features a progressive coil structure, which helps reduce initial compression stress, resulting in smoother gearbox operation and improved mechanical longevity.

An M105 rating generally corresponds to approximately ~330–360 FPS (0.20g BBs) depending on air seal quality, barrel length, and overall internal efficiency. This makes it a popular mid-power option for outdoor AEG setups where a balance between range, accuracy, and gearbox stress is required.

It is compatible with most standard V2 and V3 AEG gearboxes, making it a straightforward drop-in upgrade for many M4, AK, and similar platforms.