Enhanced Power Buffer Spring. The design loads of the Blue spring are approximately 15% 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. We were encouraged to manufacture the Blue spring by Mike Pannone of CTT Solutions, who modified one of Sprinco's Red springs and recommended that they offer a spring with the loads of the Blue spring to address the high performance demands of other specimen platforms. While contemporary internet forum lore leans towards the use of the Blue spring with an H2 or ST-T2 buffer for 14.5 - 16" ML carbines, nothing Mfg: Sprinco Usa