The 6354RDSO holster is designed for firearms with red dot sights. Its Automatic LockingSystem (ALS) secures the firearm. Unlike Safarilands RDS series, the RDSO has an open pocket that protects the optic and does not use a flip-up dust cover. Safariland cannot guarantee that RDS holsters will be compatible with non-factory(Glock MOS, M&P CORE, etc.) mounted red dots. Numerous variables, including placement of the RDS on the slide, use of dovetails, can affect the fit.