After the US Army cancelled the Individual Carbine competition in 2013 it was pretty much decided that the M4A1 design will soldier on for at least another decade before serious efforts begin to find a replacement for it. By the time that happens, there’s a good chance the competition entrants will be in a different, probably larger, caliber. In the meantime, it’s worth looking at whether the Army should be contemplating a new carbine at all, or if it would be better returning to the rifle format.
Traditionally a carbine was a short-barreled version of the service rifle issued to supporting troops as a defensive weapon – the original users were artillerymen and cavalry. Meanwhile, the infantry relied on the longer range and heavier punch of a rifle, which was their primary weapon for both offense and defense. The US Army has now turned that on its head. The M4 will eventually replace all M16s in the Army but they were issued to the infantry first, while other specialties were left with rifles until enough carbines were procured. The USMC isn’t as convinced this is the way ahead – while they do use the M4, the primary weapon of a Marine rifleman remains the latest version of the M16A4.
So what’s prompted the Army to go down this path? Mostly it seems to have been the experience of Iraq, where the short M4 proved to be a very handy weapon in urban combat. There’s no doubt that, at 6 inches shorter than an M16, it’s easier to maneuver through doors and handle in a vehicle. Unfortunately this compactness comes at a price.
It’s been known since the early days of Vietnam that the effectiveness of the tiny 5.56mm bullet comes from its high velocity. Lopping nearly a third off the barrel reduces this velocity substantially – from 3,050fps to 2,900fps. That doesn’t seem like much, but the kinetic energy of a bullet increases with the square of its velocity, so the energy loss is much greater. At lower velocities, the bullet also doesn’t fragment as reliably, and often just drills a neat hole in the target. The result is that while the M16 is effective out to about 330 yards, the M4 can’t drop enemies reliably beyond 150. And as the urban warfare of Iraq gave way to the open fields and high mountains of Afghanistan, that became a problem.
There are various solutions to this issue either in service or under evaluation, including improved 5.56mm ammunition. However, with the M855A1 it’s likely the little bullet has been developed as far as it can go. Alternative weapon layouts are another option. The British L85A2 is shorter than an M4 with the stock extended, but has a longer barrel than an M16. On the other hand, bullpups have their own issues, mostly ergonomic, and the L85 in particular is a very heavy weapon for what it does.
As always with infantry weapons, the argument returns to heavier calibers – thousands of 7.62mm M14-series rifles have been reissued during the Afghan operation, many of them modified with shorter barrels, and the British SAS are enthusiastic users of the HK417 with barrels as short as 13 inches. The reason is simple – heavier rounds gain more of their energy from weight, and retain more power and range when fired through a shorter barrel. It’s generally agreed that 7.62 NATO is overkill for the average infantryman, but if the US Army wants to stick with carbines, something bigger than 5.56mm is definitely going to be required in the next generation.
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