This bolt is a direct replacement for the Eclipse ETek EGO bolt constructed entirely of delrin so it is extremely light-weight.The bolt has an "cupped face" for high air flow and an angled inlet to promote laminar air flow. This bolt is new and is a direct replacement for the marker listed above. Other features include ramped nose, full length and depth ball detent grooves, and a dual o-ring patteren designed for max efficiency with mininal drag. Please e-mail any questions to info@alamocitypb.com