The PDI SS5000 Spring for Airsoft Bolt Action Rifles is now available at the X-Fire online store and is renowned as one of the most powerful spring series on the market. Originally developed for the Super 9 Pro, these springs are compatible with various bolt action rifles, including the APS-2, Type96, M40XB, and VSR-10. They feature a 13mm outer diameter and an 11mm inner diameter, requiring a 9mm spring guide and a piston with a 13mm inner diameter.