Built by Rheinmetall Landsysteme of Germany, 120mm M256 smoothbore gun installed onto late-1980s M1A1 and early-1990s M1A2 versions (original 1980s M1 versions mounted M68A1 105mm rifled gun). Comparing the two types, smoothbore guns cannot impart rotation to stabilize artillery round as it leaves the barrel (thus requiring the ammunition to have directional nozzles or fin stabilizers during flight). However, it can fire rounds at higher velocity without barrel damage and employ a wider variety of ammunition. Rheinmetall Ammunition & Weapon Systems for Ground Forces - www.army-technology.com/contractors/ammunition/rheinmetall/index.html

Specialized ammunition includes M829 Sabot and M8300 HEAT rounds. Sabot (French word for "clog") is a depleted-uranium explosive arrow warhead wrapped in a metal jacket. When fired, metal jacket falls away, warhead arrow impacts the target in a small area. Its uranium tip (denser than steel armor thus packing more kinetic energy) will penetrate the target and spew molten fragments into the crew compartment. Sabot - en.wikipedia.org/wiki/Sabot

HEAT (High Explosive Anti Tank) round is a shaped-charge warhead. When impacted against the target, its explosive tip melts surrounding metal and spew hot gas and molten fragments into the vehicle. High Explosive Anti Tank - en.wikipedia.org/wiki/High_explosive_anti-tank

Rifled and Smooth Bore guns have different barrel designs. Rifled gun has internal circular grooves cut along the barrel's inner walls, thus imparting a spin to its shells during firing, thus enhances accuracy and flight stability. By mid-1950s, tanks needed to fire wider ammunition variety (ex. enhanced-range, combustible cases, illumination, smoke), thus smooth bore guns were introduced. This gun type does not have internal grooves, but its ordnances have fin or jet nozzle components for flight stability. Tank gun - en.wikipedia.org/wiki/Tank_gun

Rollover : Rheinmetall's 120mm gun close-up, large bulge in barrel center is the evacuator's tube for drawing out excess gases during firing. This prevents exhaust from spewing out immediately after shell departure, which can temporary blind the tank view. Exhaust fumes result from partially burnt ignition powder inside the barrel. One solution to barrel exhaust and bulky shell casings (containing both warhead and solid propellant) is to use aerosol ignition source inside the barrel, thus requiring the tank to carry only shell warheads. Rheinmetall 120 mm L44 Tank Gun - www.rheinmetall-detec.de/index.php?fid=1448&lang=3&pdb=1

• Rheinmetall 120 mm Gun - en.wikipedia.org/wiki/Rheinmetall_120mm_Gun

Six-barrel M250 smoke grenade dischargers mounted on turret sides in armored casings. Sighting optics includes daylight, thermal imaging, and light-ambient technologies. Daylight optics are powerful binoculars with 3 to 10 times magnification, its effectiveness can be undermined by environmental conditions (ex. fog, rain) or enemy defenses (ex. smoke). Abrams Black and White Line Art - www.tankmastergunner.com/abrams%20bw%20art.html

Thermal imaging is based on object's heat differentials, digitally interpreted by the system into multi-color scale image. Objects radiating more heat are contrasted in brigther colors. Equipment is versatile in all environmental and most enemy countermeasures, hence it is the defacto sighting option used by Abrams crew. Thermal Imaging - en.wikipedia.org/wiki/Thermal_imaging

Light-Ambient optics gather surrounding light source (ex. sun, moon, stars, street lights) to amplify the image, digitally interpreted by the system as contrasting green or gray scale image. Its effectiveness can be defeated from insufficient light sources (ex. moonless night) or enemy defenses. Electro-Optical Imaging System - www.fas.org/man/dod-101/navy/docs/es310/EO_image/EO_Image.htm