Picatinny rail
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Picatinny rail on a Steyr HS50, with and without an attached telescopic sight
The HK416 is equipped with a proprietary accessory rail forearm with MIL-STD-1913 rails on all four sidesThe Picatinny rail (IPA: /ˈpɪkətɪni/ or /ˌpɪkəˈtɪni/) or MIL-STD-1913 rail is a bracket used on some firearms in order to provide a standardized mounting platform. The name comes from the Picatinny Arsenal in New Jersey, where it was originally tested and was used to distinguish it from other rail standards at the time. The rail comprises a series of ridges with a T-shaped cross-section interspersed with flat "spacing slots". Scopes et al. are mounted either by sliding them on from one end or the other; by means of a "rail-grabber" which is clamped to the rail with bolts, thumbscrews or levers; or onto the slots between the raised sections.
The rail was originally for scopes. However, once established, the use of the system was expanded to other accessories, such as tactical lights, night vision devices, laser sighting modules, reflex sights, fore grips, bipods, and bayonets. Because they were originally designed and used for telescopic sights, the rails were typically found only on the receivers of larger caliber rifles. But their use has extended to the point that today the combination of Picatinny rails and accessories are displacing the original iron sights in the design of many firearms, and they can now often be found on the undersides of frames and even on grips.
Picatinny Rail Dimensions, Cross Section (dimensions in inches)
Picatinny Rail side view (dimensions in inches)In order to provide a stable platform, the rail should not flex as the barrel heats and cools; this is the purpose of the spacing slots: they give the rail considerable room to expand and contract lengthwise without distorting its shape. The Picatinny locking slot width is 0.206 in (5.232 mm). The spacing of slot centers is 0.394 in (10.008 mm) and the slot depth is 0.118 in (2.997 mm).[1] The only differences between the Picatinny rail and the similar Weaver rail are the size of these slots and the fact that they are standardized. Weaver rails have a slot width of 0.180 in (4.572 mm), but are not necessarily consistent in the spacing of slot centers.[2] Because of this, accessories can be and are designed to fit on both Weaver rails and Picatinny rails; but most Picatinny devices will not always fit on Weaver rails.[2]
