Stern Defense MAG-ADMP9&40/P320 AR-15/M4/M16 Magazine Conversion Adapter M&P 9mm/.40S&W Black 001-SD MAG-AD-9AND40-M. 40 S&W M&P and P320/P250 Magazines The Mag-AD series adapters install in seconds. Boasting a last round hold open feature making them...