AR Maglock Gen 4 AR-10 - .308 - Narrow Rec Width/Shorter Length Shaft - For narrow width .308 receivers - Use this one if you possess Aero Precision M5, DPMS, S&W M&P, Troy, Wilson Combat, CMMG Mk3, LMT, JD Machine, SLR Rifleworks, Windham, Stag Arms