DPM FN 509 Compact MRD Upgraded Recoil Spring 3.7in Barrel Stainless. The system includes 4 external springs 2 x 1.0 mm wire diameter and 2 x 1.15mm wire diameter all with different power rates. The soft springs are designed to serve threaded barrels and compensator modifications. Specifications for DPM FN 509 Compact MRD Upgraded Recoil Springs: Manufacturer: DPM Color: Stainless Fabric/Material: Oxide Stainless Steel Gun Make: FN Herstal Gun Model: FN 509 Compact Projectile Caliber: .355 Caliber Features of DPM FN 509 Compact MRD Upgraded Recoil Springs Faster follow up shots Improved firing speed Slide and Frame Protection Elimination of jams Significant recoil reduction Better double-tap concentration Better control and greater accuracy Package Contents: DPM FN 509 Compact MRD Upgraded Recoil Springs What firearm models does the manufacturer say DPM FN 509 Compact MRD Upgraded Recoil Springs is compatible with? The manufacturer suggests that DPM FN 509 Compact MRD Upgraded Recoil Springs is compatible with FN 509 CompactDPM MS-FNH/4: FN 509 Compact MRD Upgraded Recoil Spring 3.7in Barrel Stainless