Editing M16 rifle (section)

==NATO standards==
In March 1970, the U.S. recommended that all NATO forces adopt the 5.56×45mm cartridge.{{sfnp|Arvidsson|2009|p=4}} This shift represented a change in the philosophy of the military's long-held position about caliber size. By the mid 1970s, other armies were looking at M16-style weapons. A NATO standardization effort soon started and tests of various rounds were carried out starting in 1977.{{sfnp|Arvidsson|2009|p=4}} The U.S. offered the 5.56×45mm M193 round, but there were concerns about its penetration in the face of the wider introduction of [[ballistic vest|body armor]].{{sfnp|Ehrhart|2009|pp=22-24}} In the end, the Belgian 5.56×45mm SS109 round was chosen ([[STANAG]] 4172) in October 1980.{{sfnp|Arvidsson|2009|p=6}} The SS109 round was based on the U.S. cartridge but included a new stronger, heavier, 62-grain bullet design, with better long-range performance and improved penetration (specifically, to consistently penetrate the side of a steel helmet at 600 meters).{{sfnp|Ehrhart|2009|pp=22-24}} Due to its design and lower muzzle velocity (about 3110&nbsp;ft/s){{sfnp|Colt, ''M16 5.56mm Rifle''|2003}} the Belgian SS109 round is considered more humane because it is less likely to fragment than the U.S. M193 round.{{sfnp|Parks|2010|pp=2}} The NATO 5.56×45mm standard ammunition produced for U.S. forces is designated [[M855]].

In October 1980, shortly after NATO accepted the 5.56×45mm NATO rifle cartridge.{{sfnp|Watters|2000|p=1}} Draft Standardization Agreement 4179 ([[STANAG 4179]]) was proposed to allow NATO members to easily share rifle [[ammunition]] and magazines down to the individual soldier level. The magazine chosen to become the ''STANAG magazine'' was originally designed for the U.S. M16 rifle. Many NATO member nations, but not all, subsequently developed or purchased rifles with the ability to accept this type of magazine. However, the standard was never ratified and remains a 'Draft STANAG'.{{sfnp|Arvidsson|2008|p=8}}

All current M16 type rifles are designed to fire STANAG [[22 mm grenade|22&nbsp;mm]] [[rifle grenade]]s from their integral flash hiders without the use of an adapter. These 22&nbsp;mm grenade types range from anti-tank rounds to simple finned tubes with a fragmentation hand grenade attached to the end. They come in the "standard" type which are propelled by a blank cartridge inserted into the chamber of the rifle. They also come in the "bullet trap" and "shoot through" types, as their names imply, they use live ammunition. The U.S. military does not generally use rifle grenades; however, they are used by other nations.{{sfnp|Mecar ''Rifle Grenades''|2006}}

The [[NATO Accessory Rail]] STANAG 4694, or Picatinny rail STANAG 2324, or a "Tactical Rail" is a bracket used on M16 type rifles to provide a standardized mounting platform. The rail comprises a series of ridges with a T-shaped cross-section interspersed with flat "spacing slots". Scopes 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, laser aiming modules, night vision devices, [[reflex sight]]s, foregrips, bipods, and bayonets.

Currently, the M16 is in use by 15 NATO countries and more than 80 countries worldwide.