Editing Colt AR-15 (section)

=== Comparison to military versions ===
The primary distinction between civilian semi-automatic rifles and military models is [[select fire]]. Military rifles were produced with firing modes, [[Semi-automatic firearm|semi-automatic fire]] and either fully [[Automatic firearm|automatic fire]] mode or [[Burst mode (weapons)|burst fire]] mode, in which the rifle fires three rounds in succession when the trigger is depressed. Most components are interchangeable between semi-auto and select fire rifles including magazines, sights, upper receiver, barrels and accessories.<ref name=gundigest/><ref>{{cite book|last1=Zimba|first1=Jeff|title=The Evolution of the Black Rifle|date=2014|publisher=Prepper Press|isbn=978-0692317266}}</ref> The military [[M4 carbine]] typically uses a {{convert|14.5|in|adj=on}} barrel. Civilian rifles commonly have 16-inch or longer barrels to comply with the [[National Firearms Act]].<ref>{{cite book|last1=Muramatsu|first1=Kevin|title=Gun Digest Guide to Customizing Your AR-15|date=2014|publisher=F+W Media, Inc|isbn=978-1440242793}}</ref>

In order to prevent a civilian semi-automatic AR-15 from being readily converted for use with the select fire components, Colt changed a number of features. Parts changed include the lower receiver, bolt carrier, hammer, trigger, disconnector, and safety/mode selector. The semi-automatic bolt carrier has a longer lightening slot to prevent the bolt's engagement with an automatic sear. Due to a decrease in mass the buffer spring is heavier. On the select fire version, the hammer has an extra spur which interacts with the additional auto-sear that holds it back until the bolt carrier group is fully in battery, when automatic fire is selected.<ref>{{cite book|last1=Hanks|first1=D. A.|title=Workbench AR-15 Project|date=2004|publisher=Paladin Press|isbn=1610048466}}</ref> Using a portion of the select fire parts in a semi-automatic rifle will not enable a select fire option.<ref name="Leghorn">{{cite web|last1=Leghorn|first1=Nick|title=Ask Foghorn: What's the Difference Between a Full Auto and Semi-Auto Only AR-15 Bolt Carrier?|url=http://www.thetruthaboutguns.com/2012/06/foghorn/ask-foghorn-whats-difference-between-full-auto-semi-auto-only-ar-15-bolt-carrier/|website=The Truth About Guns|date=June 27, 2012|publisher=THETRUTHABOUTGUNS.COM|access-date=March 6, 2018|archiveurl=https://web.archive.org/web/20170711032652/http://www.thetruthaboutguns.com/2012/06/foghorn/ask-foghorn-whats-difference-between-full-auto-semi-auto-only-ar-15-bolt-carrier|archive-date=July 11, 2017}}</ref>{{Better source needed|date=October 2024}} As designed by Colt the pins supporting the semi-auto trigger and hammer in the lower receiver are larger than those used in the military rifle to prevent interchangeability between semi-automatic and select fire components.<ref>{{cite book|last1=Sweeney|first1=Patrick|title=Gunsmithing the Ar-15, the Bench Manual|date=2016|publisher=F+W Media, Inc|isbn=978-1440246609}}</ref>