Without getting into too much Milspeak techno-history let's just say that the Picatinny rail system (MIL-STD-1913 or STANAG 2324) from ATK started out as a modification of the Weaver railing of the 1980s that sought to eliminate iron sights altogether on rifles. The Weaver railing allowed standardization as a scope mount and later accessories for rifles on almost any type and some auto-pistols like Walther types. The Picatinny railing is a modification with larger locking slots which can take a wide range of accessories on all 4 sides: various optical scopes, night vision devices, tac lights, laser designators, foregrips, and bayonets... While many Weaver accessories can generally fit the Picatinny system, the same is not true for the opposite system. Highly successful, PIcatinny is used in the civilian and military sectors with citizens, police, soldiers, HRUs, and SFs on their weapons.