Anttech Airsoft Studios does a comprehensive guide on upgrading the S&T Cyber Gun Featherweight M249 for airsoft, transforming it from a budget-friendly option into a high-performing LMG. The base gun is affordable but requires significant upgrades to perform well, with the upgrading potentially costing more than the gun itself. Key upgrade areas include the gearbox shell, HPA engine (F2 with a #14 nozzle is recommended), outer barrel, feed block (Anttech improved feed block), hop-up and barrel assembly (Bullgear hop-up chamber), bucking (EMG Atlas), and box magazines (Bullgear kit mags). Detailed instructions are provided for installation and tuning, emphasizing proper nozzle alignment and air seal. The guide also covers power configuration, suggesting a single battery for both the magazine and the gun, and customization options for outer barrels, stocks, and other accessories.