Volquartsen Firearms SureFeed Magazine Follower Spring Ruger 22/45 MK IV 2/ Pack. The increased spring rate improves feeding in all Ruger MKIII and MK IV magazines. The SureFeed Magazine Follower Spring will eliminate feeding issues caused by the round either being stuck or slow to feed from the magazine. This happens during both slow and rapid fire. Specifications for Volquartsen Firearms SureFeed Magazine Follower Spring for Ruger MK IV: Manufacturer: Volquartsen Firearms Color: Silver Gun Model: Ruger Mark IV 22/45 Condition: New Country of Origin: USA Gun Make: Ruger Package Contents: Volquartsen Firearms SureFeed Magazine Follower Spring for Ruger MK IV What firearm models does the manufacturer say Volquartsen Firearms SureFeed Magazine Follower Spring for Ruger MK IV is compatible with? The manufacturer says that Volquartsen Firearms SureFeed Magazine Follower Spring for Ruger MK IV is compatible with Ruger Mark IV 22/45Volquartsen Firearms VC4FS-2: SureFeed Magazine Follower Spring Ruger 22/45 MK IV 2/ Pack