M4 Carbine
The ageing M4 carbine is being replaced by the M27 automatic assault rifle Joe Raedle/Getty Images

The US Marine Corps has decided to increase its usage of the M27 automatic assault rifle and will begin issuing the upgraded weapon in place of the ageing M4 Carbine. The M27 Infantry Automatic Rifle will be given to Marines in combat-related operations.

Almost all frontline Marines will get an M27, reported Popular Mechanics (PM), as they have found this rifle sufficiently better than the M4 – enough to cough up the additional cost of $3,000 (£2,165) per rifle. According to reports, every Marine in an infantry squad will get this weapon.

While the Marines adopted the M27 in 2010, the report mentioned that it was provided to only one Marine per infantry fire team, or three per squad. The rifle replaced the M249 at the time.

The M27 is famed for its capacity to fire accurate, short bursts of suppressive fire at the enemy at distances that are more than what was achievable by the M249 which is a less accurate but fast-firing and high-capacity weapon.

General Robert Neller, Commandant of the Marine Corps, said that "forward observers, fire support teams and engineers" are also appropriate candidates for the M27, apart from Marines in the infantry squad. He also added that Javelin anti-tank missile operators and mortarmen would continue to use M4s for now.

Manufactured by Heckler & Koch, the M27 is a 416 assault rifle that is similar in its outward appearance to the M4 Carbine, noted PM. The differences between the rifles, however, are all internal, specifically in the way the bolt is driven. The M27 uses a piston operating system, while the M4 Carbine has a gas impingement system. As a result, the M27 is a cleaner, 'cooler to the touch' rifle. It recycles hot gases right back into the action to cycle the bolt.

Apart from the way the M27 fires, its accuracy reportedly makes it a lot more attractive. Its slightly longer and thicker barrel gives it extra range and the gun has less chances of overheating when compared to the M4. Also, the barrel is free-floating, meaning it makes contact with the rest of the rifle only at the receiver, and this reportedly prevents the gun's accuracy from degrading as the weapon heats up over repeated firing.

All of these attributes make the weapon accurate by up to 600 yards – 100 yards further than the M4. The accessories that go with the gun include a Trijicon ACOG Squad Day Optic and a folding bipod, reported PM.

In spite of all these differences, both the M4 and M27 use the same ammunition. So the introduction of a new weapon to a large part of the Marine Corps in battle should not cause too many complications, and the military can keep both rifles in service at the same time, noted the report.