Editing Automatic rifle (section)

===5.56mm NATO===
[[File:7.62x51 and 5.56x45 bullet cartridges compared to AA battery.jpg|thumb|The [[7.62×51mm NATO]] and 5.56×45mm NATO cartridges compared to an [[AA battery]].]]
The adoption of the M16, the H&K33, and the 5.56×45mm cartridge inspired an international trend towards relatively small-sized, lightweight, high-velocity military service cartridges that allow a soldier to carry more ammunition for the same weight compared to the larger and heavier [[7.62×51mm NATO]] cartridge. The 5.56mm cartridge is also much easier to shoot.<ref name="AGWilliams-Ammo" /><ref name="auto">{{cite web|url=http://www.ar15.com/content/page.html?id=599 |title=An Improved Battlesight Zero for the M4 Carbine and M16A2 Rifle |access-date=2007-09-11 |archive-url=https://web.archive.org/web/20140122215037/https://www.ar15.com/content/webPDF/TM9-1005-319-10.pdf |archive-date=2014-01-22 |url-status=dead }}</ref><ref name="auto1">{{cite web|url=https://www.ar15.com/content/webPDF/TM9-1005-319-10.pdf |title=TM 9-1005-319-10 (2010) - Operator's Manual for Rifle, 5.56 MM, M16A2/M16A3/M4 (Battlesight Zero pages 48-55)|access-date=2014-06-03}}</ref> In 1961 marksmanship testing, the U.S. Army found that 43% of [[ArmaLite AR-15]] shooters achieved Expert, while only 22% of M-14 rifle shooters did so. Also, a lower [[free recoil|recoil]] impulse allows for more controllable automatic weapons fire.<ref name="AGWilliams-Ammo" /><ref name="auto"/><ref name="auto1"/>

Therefore, in March 1970, the U.S. recommended that all [[NATO]] forces adopt the [[5.56×45mm]] cartridge.<ref name="autogenerated3">Per G. Arvidsson [https://web.archive.org/web/20091229100726/http://www.dtic.mil/ndia/2009infantrysmallarms/wednesdaysessionvArvidsson.pdf Weapons & Sensors]. NATO Army Armaments Group</ref> This shift represented a change in the philosophy of the military's long-held position about caliber size. By the middle of the 1970s, other armies were looking at assault rifle type weapons. A NATO standardization effort soon started and tests of various rounds were carried out starting in 1977.<ref name="autogenerated3"/> 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]].<ref name="ReferenceA"/> In the end, the Belgian 5.56×45mm SS109 round was chosen ([[STANAG]] 4172) in October 1980.<ref name="autogenerated3"/> 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).<ref name="ReferenceA"/>

During the 1970s, the USSR developed the [[AK-74]] and the [[5.45×39mm]] cartridge, which has similar physical characteristics to the U.S. 5.56×45mm cartridge.<ref name="HoggWeeks271">{{cite book|last1=Hogg|first1=Ian V.|last2=Weeks|first2=John|title=Military Small Arms of the 20th Century|edition=7th|publisher=Krause Publications |year=2000|page=271|isbn=978-0-87341-824-9}}</ref> Also during the 1970s, Finland, Israel, South Africa and Sweden introduced AK type rifles in 5.56×45mm.<ref>{{cite book|last1=Hogg|first1=Ian V.|last2=Weeks|first2=John|title=Military Small Arms of the 20th Century|edition=7th|publisher=Krause Publications |year=2000|pages=235, 258, 274, 278|isbn=978-0-87341-824-9}}</ref> During the 1990s, the Russians developed the [[AK-101]] in 5.56×45mm NATO for the world export market.<ref name="ReferenceB">[https://web.archive.org/web/20110718230910/http://www.izhmash.ru/eng/product/weapon.shtml LEGION Ltd. – the producer of high-quality firearms with period artistic treatment (threading, engraving, incrustation) and improved finishing]. izhmash.ru</ref><ref>{{Cite web |title=Kalashnikov AK-101 |url=https://www.militaryfactory.com/smallarms/detail.php?smallarms_id=256 |access-date=2023-06-20 |website=www.militaryfactory.com}}</ref> In addition, Bulgaria, Czechoslovakia, Hungary, Poland and former countries of Yugoslavia have also rechambered their locally produced assault rifle variants to 5.56mm NATO.<ref>{{cite book|last1=Hogg|first1=Ian V.|last2=Weeks|first2=John|title=Military Small Arms of the 20th Century|edition=7th|publisher=Krause Publications |year=2000|pages=233, 257, 266, 296|isbn=978-0-87341-824-9}}</ref><ref>{{cite web|url=http://www.arsenal-bg.com/defense_police/5.56_arsenal_assault_rifle_ar-m1_ar-m1f.htm |title=Arsenal 5.56mm Arsenal Assault Rifle AR-M1and 5.56mm Arsenal Assault Rifle AR-M1F |access-date=2014-06-10 |url-status=dead |archive-url=https://web.archive.org/web/20140618165043/http://www.arsenal-bg.com/defense_police/5.56_arsenal_assault_rifle_ar-m1_ar-m1f.htm |archive-date=2014-06-18 }} | Arsenal AR-M1 5.56mm assault rifle</ref> The adoption the 5.56mm NATO and 5.45×39mm cemented the worldwide trend toward small caliber, high-velocity cartridges.