Soldiers, special operators and Marines in the near future will carry a first-of-its kind rifle and light machine gun that fires a bullet created to overcome decades of previous small arms limitations.

The Next Generation Squad Weapon program gives U.S. troops a far more lethal 6.8 mm round following the 40 years the Pentagon has spent searching for an alternative to the 5.56 mm round that troops have been taking to war for the past 65 years.

U.S. infantry squads carrying 5.56 mm rifles and light machine guns currently face an overmatch. If those squads went into a firefight with Russian, ­Chinese or most Kalishnokov-wielding militants, they’d be outgunned in both distance and lethality.

Most potential world adversaries carry 7.62 mm weapons with ranges of 1,000 meters to 1,500 meters. U.S. units’ deepest small arms range is 800 meters to 1,100 meters. And those distances are only reached by the designated marksman and platoon-level machine gunners.

With the new, 6.8 mm-chambered long guns, everyone in the squad will be able to shoot fewer rounds farther and with more devastation on targets than they can now — bringing a heavier, but more accurate and powerful weapon to bear in ­close-combat fighting, Army officials said.

This program is the first to produce a viable weapon on deck for mass production and fielding. A not-yet-identified Army unit is expected to receive the NGSW-rifle and NGSW-automatic rifle, the XM5 and XM250, which eventually will be called the M5 and M250, by or before October 2023.

The change is substantial.

The Army chooses a new weapon system to replace M-4s and M-249s among troops over the coming years.

Issuing a high-velocity round and lighter rifle with the 5.56 mm and M16 to troops in the Vietnam War and beyond meant more rounds to fire with less recoil. But the change also meant shooters couldn’t kill targets consistently past 300 meters.

The new 6.8 mm round fills gaps between the 5.56 mm and the 7.62 mm, the heavier round troops use in medium machine guns and older sniper rifles, officials said.

The move isn’t cheap. In the next decade the two weapon variants alone could cost as much as $4.7 billion, while the NGSW fire control, or M157 advanced optic, will cost another $2.7 billion, ­according to official documents. Those dollar amounts are more typical for tanks, jet fighters or ships.

Army leaders in recent years have pushed against the limited funding close combat forces receive, ­especially when considering the disproportionate number of casualties and fatalities that part of the force absorbs in combat.

The two weapons should reach an Army unit by 2023. But the bulk of the close combat force will have to wait. Production work, annual budgets and implementation of training and fielding plans all mean that the 120,000 close combat forces in the Army will not see a full fielding of the weapon for at least a few years or as much as a decade.

Army 11B infantryman, 19D cavalry scouts,12B combat engineers, 68W combat medics and 13D forward observers are on the list for NGSW deliveries. The rest of the Army will continue carrying the M4 and M249 SAW for the next few decades, officials said.

Marines and Marine Raiders participated in ­multiple testing events, and Corps officials said that the service is monitoring the Army program but had not yet decided whether to adopt the weapon system or ammunition.

What’s different?

The NGSW program sought an “intermediate caliber” — a heavier and longer range projectile than the 5.56 mm but lighter and more manageable than the 7.62 mm.

The Pentagon provided its own, ­government-designed projectile, the 6.8 mm bullet, to weapons companies.

From there, three semi-finalist competitors — Sig Sauer, Textron Systems and Lone Star Future ­Weapons in partnership with General Dynamics, built solutions. The winner, Sig Sauer, built a more traditional assault rifle design, with many of the same ergonomic features and feel of the existing M4.

Sig Sauer also won the handgun replacement contract for all of the services in 2017.

Program Executive Office-Soldier and the Army Futures Command Cross Functional Team-Soldier Lethality have run the NGSW program, with ample input from Program Executive Office-Ammunition and the lethality branch at the Maneuver Center of Excellence.

Ultimately, XM5 shooters will give up 70 rounds and carry another 5 pounds in total weapon, optic and ammo load compared to the M4. XM250 light machine gunners will lose 200 rounds and add a net weight amount of 3.6 pounds compared with the M249 SAW load. The XM250 is a lighter weapon but the ammo is heavier and the new optic adds 2.6 pounds to the system.

The combined accuracy and effectiveness of the weapon, ammunition and optic should mean fewer rounds needed to strike and incapacitate a target, officials said.

Detailed data of the round’s performance in testing are classified, according to responses to media queries.

The system delivers, “probability of incapacitation (overmatch) against the full array of target sets the Close Combat Force will encounter in current and future Large Scale Combat Operations,” Bridget Siter, CFT-SL spokeswoman told Marine Corps Times.

“The effects achieved by the NGSW system on first round hits would likely take our current weapons multiple rounds to achieve,” Siter wrote.

The final weapon design and ammunition features are still being refined.

Due to federal contracting rules, Army entities such as Program Executive Office Soldier and

Army ­Futures Command were restricted from detailed ­contact with the vendors during prototype selection, said Bridgett Siter, CFT-SL spokeswoman. Combinations of bullet, powder and cartridge configuration and small items on the weapon could be adjusted as the Army fits the ammo and weapon together in the manufacturing.

The history

From its inception, the 5.56 mm round and the M16 service rifle were controversial.

The caliber was used within small game hunting ­circles and was a major departure for small arms. It was a shift that stopped the use of the heavier ­.30-caliber family ammunition common among ground combat troops beginning in World War I.

Developed in the late 1950s by Eugene Stoner, the M16 rifle was first fielded by the Air Force. The Army adopted the M16A1 in 1967 to replace the 7.62 mm M14 rifle.

Controversy centered around the performance of lighter rounds when compared with heavier rounds. Shooters claimed that lighter rounds lacked “­stopping power,” an elusive metric for determining a round’s effectiveness.

But advocates pushed for a lighter round that would add more shots and give a greater volume of fire. Leaders also saw a chance for better accuracy because of the reduced recoil.

The U.S. military, NATO and at least 85 countries fielded the M16. Over the decades, multiple ­programs sought to replace the M16 and its later carbine variant, the M4.

Those included the early 1980s advanced combat rifle program, the early 2000s objective individual combat weapon, or XM29, and a subsequent ­program known as XM8, which had optics

built into the weapon. None of those long gun programs succeeded.

Early in the Afghanistan War, U.S. troops ­complained about the 5.56 mm caliber’s limited range, which prompted development and fielding of an improved 5.56 mm round in 2010.

Advances in body armor that could withstand the 5.56 mm round eventually pushed researchers to launch the Small Arms Ammunition ­Configuration Study.

That study, began in 2014 and published in 2017, resulted in the Army choosing to look for its ­replacement in the 6 mm range.

Early experiments included the .260 R­emington, 6.5 mm Creedmoor and .264 USA rounds as ­contenders, Army Times reported in 2017. But rather than go with a commercial round, the Army chose instead to produce its own projectile, based on work done by engineers and shooters at the Army ­Marksmanship Unit.

The M1 Garand rifle, fielded to troops in World War II was first built in both .30-caliber and .2760-caliber versions. Though the .276 performed better, large stocks of .30-caliber ammunition left over from World War I drove budget-conscious arms developers to choose the .30-caliber option.

The Marine Corps found its own commercial replacement for the M4, at least for infantry and reconnaissance Marines, in recent years. And it stuck with 5.56 mm rounds.

In 2010, the Corps began fielding the M27, a 5.56 mm infantry automatic rifle, to replace both the SAW and M4.

Marines and Special Operations Command troops participated in testing and evaluating the NGSW prototypes. The 10-year contract for the weapon has allotted 120,000 rifles or automatic rifles for the Army but has capacity to build another 130,000 for Marines, SOCOM and foreign partner sales, officials said.

When asked about work with the NGSW and ­fielding plans, Marine Corps Systems ­Command spokeswoman Kelly Flynn said the Corps, “­continues to assess NGSW solutions for maturity, suitability and affordability to meet our operational requirements.”

The Corps’ M27 IARs will reach the service life ­limit by 2031. There is not a follow-on M27 ­replacement in the works other than Marine Corps monitoring of the NGSW program, Flynn said.

More work, changes and an optic

Beyond the new caliber and weapon design, more ­options will be available to shooters. Though the Army, Sig Sauer and the service’s main supplier of ammunition all have a lot of work to do first.

The new ammo will replace part, but not all, of the small arms ammo the Army needs. For now, Sig Sauer will run a 6.8 mm production line at its New Hampshire facility.

As production ramps up, the Lake City Army Ammunition Plant near Independence, Missouri, will add a new line and building exclusively for 6.8 mm ammunition.

But the facility isn’t expected to be running at full capacity until fiscal year 2025 at the earliest, said Army Brig. Gen. William M. Boruff, who is with the Joint Program Executive Office-Armaments and Ammunition.

The Army must produce a “war time” stockpile of ammunition. That means enough ammo for ­training and routine deployments must be made before the military can fully field the weapon to the force, Boruff said.

He did not provide detailed numbers.

Shooters will receive the new weapon with a ­suppressor and a one-of-a-kind fire control optic, the M157.

That optic combines many devices into one piece of gear. Currently, shooters attach a standard glass optic to their weapon and add on infrared or other aiming lasers to get on target. But if they want to calculate ballistics or gauge atmospheric conditions, they’ll need to tote more devices.

The M157 NGSW fire control weighs 2.6 pounds, including the remote and batteries.

The optic has an infrared and visible laser built in, as well as a ballistic calculator, atmospheric sensor suite, a compass and a digital display overlay.

The Army has a working weapon that fits its stated needs to replace the M4 and SAW for close combat. But further adjustments to optimize the round, ­weapon and optic combination will happen in the coming months and years.

To see how the XM5 may develop, look no further than the M4A1 carbine, which is dramatically ­different than the original M16 service rifle. The weapon has seen hundreds of modifications since its fielding more than half-a-century ago.

The first batch of about two dozen rifles and ­automatic rifles are expected to roll off the Sig Sauer line in the coming months. Those weapons will get recommended tweaks as the Army pushes to equip its first unit by October 2023.

Todd South has written about crime, courts, government and the military for multiple publications since 2004 and was named a 2014 Pulitzer finalist for a co-written project on witness intimidation. Todd is a Marine veteran of the Iraq War.