Editing M1 Abrams (section)

====M256 smoothbore gun====
The main armament of the M1A1 and M1A2 is the M256 120&nbsp;mm smoothbore gun, designed by Rheinmetall AG of Germany, manufactured under license in the U.S. by [[Watervliet Arsenal]], New York. The M256 is an improved variant of the [[Rheinmetall 120&nbsp;mm gun|Rheinmetall 120&nbsp;mm L/44 gun]] carried on the German [[Leopard 2]] on all variants up to the Leopard 2A5, the difference being in thickness and chamber pressure. Leopard 2A6 replaced the L/44 barrel with a longer L/55. Due to the increased caliber, only 40 or 42 rounds are able to be stored depending on if the tank is an A1 or A2 model.
* Elevation: −9 to +20 degree

[[File:US Army M1 Abrams exercise.ogv|thumb|left|M1 Abrams during a U.S. Army firing exercise, displaying internal crew cabin operations.]]
[[File:M1 Abrams turret fire above.jpg|thumb|left|An M1A1 firing its main gun as seen from the loader's hatch in joint exercises with the [[French Foreign Legion]].]]
The M256 fires ammunition with combustible cartridge cases made out of [[nitrocellulose]]. The cartridges were safer against premature ignition and flarebacks than earlier combustible cartridge rounds, but not entirely accident-proof.{{sfn|Green|Stewart|2005|p=62-65}}
The M256 fires a variety of rounds. The primary APFSDS round of the Abrams is the depleted uranium [[M829]] round, of which four variants have been designed. [[M829#M829A1|M829A1]], known as the "Silver Bullet", saw widespread service in the Gulf War, where it proved itself against Iraqi armor such as the T-72. The [[M829#M829A2|M829A2]] APFSDS round was developed specifically as an immediate solution to address the improved protection of a Russian [[T-72]], [[T-80]]U or [[T-90]] main battle tank equipped with [[Kontakt-5]] explosive reactive armor (ERA).<ref name=autogenerated1/>

Later, the [[M829#M829A3|M829A3]] round was introduced in 2002 to improve its effectiveness against next-generation ERA equipped tanks.{{sfn|Green|Stewart|2005|p=70}} Development of the [[M829]] series is continuing with the [[M829#M829A4|M829A4]] currently entering production, featuring advanced technology such as data-link capability.<ref>{{cite web|title=Next-Gen 120&nbsp;mm Tank Killer: ATK's M829E4 AKE |url=http://www.defenseindustrydaily.com/Next-Gen-120mm-Tank-Killer-ATKs-M829E4-AKE-06995/|publisher=Defense Industry Daily |url-status=live|archive-url=https://web.archive.org/web/20110716123723/http://www.defenseindustrydaily.com/Next-Gen-120mm-Tank-Killer-ATKs-M829E4-AKE-06995/|archive-date=16 July 2011}}</ref>

The Abrams also fires HEAT warhead shaped charge rounds such as the [[M830]], the latest version of which ([[M830#M830A1 HEAT MP-T|M830A1]]) incorporates a sophisticated multi-mode electronic sensing [[Fuse (explosives)|fuse]] and more fragmentation that allows it to be used effectively against armored vehicles, personnel, and low-flying aircraft. The Abrams uses a manual loader, who also provides additional support for maintenance, observation post/listening post (OP/LP) operations, and other tasks.

The new M1028 120&nbsp;mm anti-personnel [[Canister shot|canister]] cartridge was brought into service early for use in the [[Timeline of the Iraq War#2003|aftermath of the 2003 invasion of Iraq]]. It contains 1,098 {{convert|3/8|in|adj=on}} tungsten balls that spread from the muzzle to produce a [[shotgun]] effect lethal out to {{convert|600|m|sp=us}}. The tungsten balls can be used to clear enemy dismounts, break up hasty ambush sites in urban areas, clear [[defile (geography)|defiles]], stop infantry attacks and counter-attacks and support friendly infantry assaults by providing covering fire. The canister round is also a highly effective breaching round and can level cinder block walls and knock man-sized holes in reinforced concrete walls for infantry raids at distances up to {{convert|75|m|sp=us}}.<ref>{{cite journal |last=Hilmes |first=Rolf |date=1 December 2004 |page=79 |title=Arming Future MBTs&nbsp;– Some Considerations |journal=Military Technology |publisher=Mönsch}}</ref>

Also in use is the M908 obstacle-reduction round. It is designed to destroy obstacles and barriers. The round is a modified [[M830#M830A1|M830A1]] with the front fuse replaced by a steel nose to penetrate into the obstacle before detonation.<ref>[http://www.atk.com/products-services/m908-he-or-t-ammunition-120-mm-2/ "M908 HE-OR-T"] {{webarchive |url=https://web.archive.org/web/20141112033858/http://www.atk.com/products-services/m908-he-or-t-ammunition-120-mm-2/ |date=12 November 2014}}. ATK.com</ref>

The U.S. Army Research Laboratory (ARL) conducted a thermal analysis of the M256 from 2002 to 2003 to evaluate the potential of using a hybrid barrel system that would allow for multiple weapon systems such as the XM1111 Mid-Range munition, airburst rounds, or [[M1147 Advanced Multi-Purpose|XM1147]]. The test concluded that mesh density (number of elements per unit area) impacts accuracy of the M256 and specific densities would be needed for each weapon system.<ref>{{cite report |last1=South |first1=Joseph T. |last2=Carter |first2=Robert H. |title=Thermal Analysis of an M256 120-mm Cannon |publisher=Defense Technical Information Center |publication-place=Fort Belvoir, VA |date=1 August 2005 |doi=10.21236/ada437279 |page=}}</ref>

In 2013, the Army was developing a new round to replace the [[M830]]/[[M830#M830A1|M830A1]], M1028, and M908. Called the [[M1147 Advanced Multi-Purpose|M1147]] Advanced Multi-Purpose [[M1147 Advanced Multi-Purpose|XM1147 Advanced Multi-Purpose]] (AMP) round, it will have point detonation, delay, and [[airburst round|airburst]] modes through an ammunition data-link and a multi-mode, programmable fuse in a single munition. Having one round that does the job of four would simplify logistics and be able to be used on a variety of targets. The AMP is to be effective against bunkers, infantry, light armor, and obstacles out to {{convert|500|m|abbr=on}}, and will be able to breach reinforced concrete walls and defeat [[ATGM]] teams from {{convert|500|to|2000|m|abbr=on}}.<ref>{{cite conference |url=http://www.dtic.mil/ndia/2012armaments/TuesdayPaulHill.pdf |conference=NDIA Joint Armaments Conference PM Panel|title=Advanced Multi Purpose (AMP) Overview and Status|last=Hill|first=Paul|date=May 2012 |url-status=dead |archive-url=https://web.archive.org/web/20121114131039/http://www.dtic.mil/ndia/2012armaments/TuesdayPaulHill.pdf|page=26 |archive-date=14 November 2012}}</ref><ref>[https://www.army.mil/article/98946/Army_developing_new_120mm_AMP_tank_round/ Army developing new 120&nbsp;mm AMP tank round]  – Army.mil, 19 March 2014</ref> [[Orbital ATK]] was awarded a contract to begin the first phase of development for the AMP [[M1147 Advanced Multi-Purpose|XM1147]] High-Explosive Multi-Purpose with Tracer cartridge in October 2015.<ref>[http://www.businesswire.com/news/home/20151008005038/en/Orbital-ATK-Awarded-16-Million-Develop-Generation Orbital ATK Awarded $16 Million to Develop Next Generation 120&nbsp;mm Tank Ammo] {{webarchive |url=https://web.archive.org/web/20151012025901/http://www.businesswire.com/news/home/20151008005038/en/Orbital-ATK-Awarded-16-Million-Develop-Generation |date=12 October 2015}} – Businesswire.com, 8 October 2015</ref> As of 2024 the round is undergoing the final testing stages, with the full-rate production decision scheduled for the end of the year.<ref>{{cite report |author1=Office of the Secretary of Defense |title=FY 2023 Annual Report - Director, Operational Test & Evaluation |date=January 2024 |pages=83–84 |url=https://www.dote.osd.mil/Portals/97/pub/reports/FY2023/other/2023annual-report.pdf |access-date=20 March 2024}}</ref>

In addition to these, the [[XM1111 Mid-Range Munition|XM1111]] (Mid-Range-Munition Chemical Energy) was also in development. The XM1111 was a guided munition using a dual-mode seeker that combined imaging-infrared and semi-active laser guidance. The MRM-CE was selected over the competing MRM-KE, which used a rocket-assisted kinetic energy penetrator. The CE variant was chosen due to its better effects against secondary targets, providing a more versatile weapon. The Army hoped to achieve IOC with the XM1111 by 2013.<ref>{{cite web|title=Clank Softly and Carry a Better Shillelagh |url=http://www.defenseindustrydaily.com/xm1111-clank-softly-and-carry-a-better-shillelagh-04544/|publisher=Defense Industry Daily |url-status=live|archive-url=https://web.archive.org/web/20110607011307/http://www.defenseindustrydaily.com/xm1111-clank-softly-and-carry-a-better-shillelagh-04544/|archive-date=7 June 2011}}</ref> However, the Mid-Range Munition was canceled in 2010 along with Future Combat Systems.{{sfn|Zaloga|2019|p=28}}