accessories can be used on either type of rail, and accessories designed for a Weaver system will generally fit Picatinny rails – although not vice versa. because the Picatinny locking slot width is vs the .180 width of the Weaver, and the spacing of slot centers is . Because of this, with devices that use only one locking slot, Weaver devices will fit on Picatinny rails, but Picatinny devices will not always fit on Weaver rails. Another difference is that Weaver rails are continuous with only two to four recoil grooves cut, while Picatinny rails have recoil grooves cut across the entire length of the rail at the above noted spacing (like a dotted line). This allows for more mounting position flexibility and also helps to neutralize expansion caused by barrel heating. See also Rail integration system References External links Weaver Optics Firearm components Alliant Techsystems