Extra Power Buffer Spring. This was Sprinco's first AR buffer spring solution that they were tasked to design back in 2006 for a Force Modernization Team to specifically address spring-related M4 carbine reliability function issues for operating challenges in the Eastern Asia Theatre. The design loads of the Red spring are approximately 25% greater than the White spring for one of the considered Load Constants in the spring design. Refer to provided tuning procedure reference documents prior to calling for recommendations for use. The Red spring is commonly used in 9mm, 6.8 SPC, 6.5 Grendel, .450 BM, .450 SOCOM, .500 Beowulf, and Colt LE6920’s specimen carbines, but certain specimen guns can deviate from the norm depending upon port values and the power factor of your chosen ammunition loads.