The 5" RecoilMaster guide rod system is used in STIi pistols with a 5-inch slide and either a bushing or bull barrell. The spring weight (light or heavy) pertains to caliber where 9mm and 38 Super pistols use a light Recoilmaster and 40 S&W and 45 ACP pistols use a heavy Recoilmaster. Recoil Systems RECOIL MASTERS & SPRINGS. The STI Recoil Master is designed to achieve softer recoil and bring the pistol back to point of aim GuideRod / One Extend the life of your weapon by installing a Sprinco Recoil Management GuideRodSystem. A secondary, or sub-spring assembly is incorporated onto a heat treated, stainless steel guiderod to cushion the slide to frame impact! Dual-spring, guiderodsystem gives smooth, gentle slide movement to significantly reduce muzzle flip and felt recoil. Proprietary, tuned springs help control muzzle Buy STI Recoil Master Guide Rod System, Government Length Bull Barrel, Light Factory replacement gun parts, accessories and gunsmithing service on most manufactures including Browning, Winchester, FN America, Beretta, Benelli Franchi, Stoeger, Remington, Bushmaster, Marlin, Sig Sauer, HK and many more. Notes - STI Guide Rods The guiderodsystem includes a guiderod, guiderod plug Recoil Master Spring [Light] not GuideRod springs: Sprinco Recoil Management GuideRodSystem is a drop-in replacement pistol guiderod for Glocks that reduces felt recoil and slide to frame impact and speeds shot to shot speed. This is a replacement for the main spring in the STI RecoilMaster guide rod system. This spring does not require replacement like a standard recoil spring. Sprinco Recoil Control GuideRodSystem is a high quality stainless guiderodsystem with a secondary spring to cushion slide to frame impact and reduce felt recoil and muzzle flip on semi-auto pistols. This is a recoil rod replacement to use with "HOT" or heavy loads(+P). Does not work well with lesser rounds.