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The Hollywood style machine-rifle that can fire for ages on full auto without reloading or melting its barrel

Change time again. You're not a SWAT door-kicker any more, but an infantryman of the (perhaps quite near) future. You carry a weapon - it's called a "machine rifle", perhaps - which is no heavier than a normal assault rifle of today. But, amazingly, you can fire long bursts on full auto as though you were in a movie without stripping all the rifling out of the bore: and then fire more long bursts without reloading, because your weapon holds easily fifty or a hundred rounds, while remaining light enough to handle easily in a close-up firefight. When it does finally run empty, no need to fret - you snap in another massive box of rounds. They're light enough that you can carry plenty.

How is this possible?

Well, it's the result of a couple of new technologies that US military boffins have successfully tested in the past year, both initially aimed at easing the life of machine gunners within infantry sections*.

A soldier from the Scots Guards pictured with a Light Machine Gun (LMG) near the village of Inzgule, Helmand, Afghanistan. Credit: Cpl Mark Webster/Crown Copyright

The Light Machine Gun. Only light in the context of machine-guns, though.

At the moment in most modern armies, one soldier in each four-man fire team carries a light machine-gun (aka Squad Automatic Weapon in some circles). As he has to hump his gun and most of his ammo himself, it certainly doesn't have a cooling water jacket around its barrel in the style of former days. Nonetheless, he's expected to fire it on full automatic as a matter of routine, if not perhaps with the gay abandon seen in the movies. It's the gunner's job in a firefight to put continuous firepower on the enemy, so keeping him pinned with his head down and allowing the gunner's team-mates to manoeuvre and win the fight (that's the theory, anyway).

The only problem is that even firing professional, short, controlled bursts, one will quite soon heat up your gun's barrel to the point where it will start to melt and become useless. Thus, modern machine guns are generally designed so that the barrel can be swiftly swapped for a spare. The gunner can thus keep on shooting while the first barrel gets a chance to cool off.

Unfortunately this means that a gunner or one of his mates has to lug around a spare barrel on top of all the other gear festooning the section: and steel gunbarrels, especially ones meant to stand up to sustained automatic fire, are heavy things.

Picatinny engineer Vinny Leto (right) holds one of the cobalt alloy barrels produced using the flow forming technique. Credit: US Army

Well that's the Hollywood gun-barrel cracked, lads. Now we just need to sort out the Hollywood mags.

US military boffins have been working on this problem for a while, though, and they think they have an answer. They want to make gun barrels out of cobalt alloy rather than steel, because cobalt is largely proof against heat and would also allow for less weight.

A cobalt-barrelled gun really could fire high-powered ammo on full automatic with the same profligacy as you see in the movies, without suffering any barrel-melting issues (although if nothing else changed, people would still struggle to carry the amount of ammo that movie protagonists often get through).

The snag with cobalt, however, is that being so tough it's very difficult to form. In particular it's very difficult to put the spiral rifling grooves down the inside of the barrel, necessary to make the bullets spin and so fly straight. Normally the rifling is cut into the bore, but this is impractical with super-tough cobalt.

However, US Army and Navy engineers (the latter interested in equipping their Marines and SEAL frogman-commandos better) believe they've cracked this. They've come up with a technique in which a cobalt tube has a hard preformed mandrel inserted into it. The tube is them compressed onto the mandrel extremely hard using rollers, causing its interior to take on the mandrel's shape. The rifling is pressed into the bore, rather than being cut.

This "flow forming" method has been used to make a gunbarrel from 50+ per cent cobalt alloy. The engineers then test-fired 24,000 rounds through it, causing it to reach temperatures of 1,100 degrees. A steel barrel would have failed under such treatment.

Military boffins at the famous Picatinny Arsenal are enthusiastic about the new technology, and expect to produce a cobalt barrel for an in-service machine gun by the end of the year. The cobalt barrelled gun, able to fire Hollywood-style long bursts without wrecking itself, is about to become reality.

But that's not all. The US Army has also recently announced successful tests of a new, lightweight portable machine-gun which fires special plastic ammunition. The gun and ammo are so much lighter than current weapons and their brass-cased cartridges that some soldiers are suggesting that every infantryman could in future pack the sort of firepower reserved today for heavy-weapons specialists.

The new Lightweight Small Arms Technologies light machine gun (LSAT LMG) with cased telescoped ammo. Credit: US Army

The machine-gun that only weighs as much as a rifle.

"I could see a whole squad carrying it," said Specialist Brandon Smith of the US Army, having participated in the trials lately, meaning that all soldiers would have such firepower in their personal weapons, not just specialists. "You would own the battlefield."

A regular light machine-gun shoots the same ammunition as the other troops' rifles, but it is normally fed from a long belt rather than a magazine with only 30 rounds, and an LMG is designed to be fired on full auto for sustained periods (though in short bursts only, or even its heavy barrel would soon fail due to overheating).

The downside of this is that the machine-gun and its belt (nowadays generally packaged in a box fitted to the gun, to prevent it flapping about and being a pain) are heavy, so much so that the gunner is at a decided disadvantage in a close-up gunfight where he needs to aim and shoot quickly while standing up. And the total load of weapon plus lots of ammo is very heavy.

Thus most soldiers are armed with assault rifles not built to deliver sustained automatic fire and holding less ammo. These lighter weapons are handier for close-in fighting and permit other kit to be carried.

But US military boffins at the famous Picatinny Arsenal have also been working on this situation for some time. Since ammo weight and bulk is much of the problem, they have come up with a new kind of ammunition: Cased Telescoped cartridges.

In a cased telescoped round, the bullet is no longer attached to the tip of a brass case full of propellant powder. The new case is shorter, fatter and made of plastic, so weighing substantially less, and the bullet is sunk into the middle of the propellant which makes the whole round shorter - it has been "telescoped". A shorter round weighs less itself, and also means that the gun's action, feed equipment etc is smaller and thus lighter as well. It's a trick originally developed for tanks, to make the turret smaller and easier to protect.

According to the Picatinny scientists, their new LMG and a thousand rounds of its plastic-cased-telescoped ammo weigh fully 20.4 pounds less than the current M249 (a version of which is also used by British troops) and a thousand ordinary 5.56mm brass cartridges. The new LMG shaves no less than 8.3 pounds off the 15.7-lb M249, coming in at just 7.4lb - actually lighter than a standard British SA80 assault rifle! This, perhaps, explains Specialist Smith's opinion that it would be reasonable for all soldiers to carry such weapons, rather than just heavy-weapons specialists.

There are other advantages: the new LMG's novel rotating chamber doesn't heat up as an M249's does, and plastic cases are more heatproof than brass ones, thus reducing or eliminating the issue of "cook off". This is where a round is chambered and then goes off immediately due to the chamber being hot from prolonged firing, regardless of whether the trigger is depressed at the time.

Specialist Brandon Smith carries the LSAT LMG one-handed. Credit: US Army

Certainly this bloke isn't finding it too heavy.

So all that's necessary now is to fit the new plastic-case-telescoped LMG with a cobalt barrel - making it even lighter - and there it is at last: a gun weighing no more than an assault rifle which hold a whole belt-full of ammo and can fire the whole lot off on full auto if you want without blowing the lands out of the bore. Truly, it would seem that the man-carried automatic weapon as envisaged by Hollywood has arrived at last. And "machine rifle" (see the footnote on the first page of this piece) would seem like the proper name for it.

*Squads, in American units.

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