The U.S. Army moved away from the heavier round during Vietnam when it discovered that the 7.62mm M-14 was too heavy for jungle warfare. Perhaps more importantly, emerging doctrine at the time dictated that the primary role of infantry was to find and fix the enemy so that they could be destroyed by airstrikes and indirect fire. Supressive fire became the norm, and soldiers could carry more of the 5.56mm rounds which allowed them to pin the enemy down for longer periods.*
*The Marine Corps briefly resisted this shift away from individual marksmanship, but eventually succumbed to the juggernaut that is the Pentagon's procurement procedures.
This new doctrine affected other NATO nations as well, and the Brits, French and Germans eventually switched over to the lighter NATO-standard round, partly for logistical synchronization and partly because NATO doctrine at the time mirrored U.S. Army combined arms action.*
*Even the Soviets got in on the act, switching from the heavy 7.62mm to the lighter 5.45mm for their new AK-74 (not to be confused with the original AK-47 widely used here in Afghanistan).
Now, according to The Times, both the British and U.S. militaries are considering switching back, apparently due to the fact that they are finding themselves outranged by Taliban fighters with older 7.62mm Kalashnikovs. As the article puts it:
The M4 and the SA80A2 work well in battles at close quarters, such as the narrow streets of Basra in southern Iraq. However, they are less effective in the rural environment of Helmand province, where the Taleban are often positioned more than 300 metres away, making them harder to hit.
Obviously, in a modern counter-insurgency fight, pinning the enemy down with a high volume of supressing fire and then anihilating them with airstrikes is problematic. Even before the new restrictions on close-air support and indirect fire, U.S. and British troops were having a very hard time successfully engaging the enemy without leveling half a village in the process. Now that the restrictions are in place, many engagements consist of a brief firefight in which the Taliban fire a few volleys from long-range and then disappear before ISAF troops can close and destroy them. We take a few casualties and the Talibs melt away. So, the thinking goes, re-equip our guys with longer-range weapons so that they can effectively engage the enemy at 300+ meters without having to rely on tactical air or artillery.
All well and good, but the article propogates a particularly annoying falsehood about Afghans in general and the Taliban in particular, namely that they somehow come out of the womb as master marksmen. This natural talent, wedded to the greater range of their favored AK-47, gives them an important edge over Coaltion forces. This, to put it simply, is bullshit.
First, Afghans can't shoot. Not naturally at birth, and not even after considerable training. Sure there are a few out there (mostly among the bad guys) who have decades of experience and have developed wicked skills with a rifle. But the vast majority of Afghans don't even know how to hold a weapon properly, much less successfully engage a target at 300+ meters. Your average Tennessee redneck has better marksmanship skills than most Taliban. Fortunately, we have a lot of Tennessee rednecks in the U.S. Army.
Second, while the Kalashnikov is well-suited to Afghanistan, being a simple, reliable and rugged weapon, it is not know for it's accuracy. A fresh-out-of-the-factory AK posseses reasonable accuracy, but there are precious few of those around here.* And, nearly every AK in Afghanistan has been rebuilt multiple times, often with hand-tooled parts from gunsmiths in Pakistan. As a result, most AKs are a hodge-podge of different parts and manufacturers. It's not unusual to find an AK with a Russian barrel, Ukrainian receiver, Chinese bolt assembly and a Pakistani firing pin, all scavenged from other weapons. The AKs vaunted interchanability notwithstanding, these weapons are hardly the pinnacle of accuracy and precision.
*A significant percentage of Kalashnikovs in Afghanistan are nearly as old or older than I am, and I was born when Afghanistan still had a king.
So let's leave aside all this hagiography that makes the Taliban seem like ten-foot tall superwarriors. They are tough, resourceful and dedicated, but they are not masters of the art of warfare, nor are the Afghans in general naturally unconquerable warriors born with a talent for fighting. By all means, switch to the 7.62 round and rediscover the virtues of well-trained marksmanship, but remember that it's tactics, not technology, that will win this fight.
After all, we have Tennessee on our side.