The Aero Precision EPC Receiver Extension Buffer Kit features Aero Precision's Enhanced Carbine Buffer Tube and their 7.7oz buffer and spring specifically optimized for use in the Aero Precision EPC. The 7.7oz EPC buffer is not intended for use in AR15 or M5 platforms. The additional length and weight will not allow for proper cycling of standard platforms. Kit IncludesEPC Buffer308 Carbine Buffer SpringEnhanced Carbine Buffer TubeMil-Spec Receiver End PlateMil-Spec Castle NutStock NOT Included Note: For use in a 40S&W, 10mm, or 45ACP build we recommend the use of a heavier buffer spring.