The Russian Army has a adopted a locally made 12.7mm sniper rifle, the 11kg (24.2 pounds) 6V7M. This is apparently mainly for “anti-material” targets, not just enemy troops. Lighter sniper rifles will continue to be used for most anti-personnel work.
The 12.mm rifle concept was pioneered by an American firm (Barrett) which introduced the first widely used one (the M82) in 1982. The M82A1 rifle used by the U.S. Army and Marines weighs 12.7 kg 28 pounds) unloaded and is 1.44 meters (57 inches) long. Lighter versions have been developed in the last two decades. In Iraq and Afghanistan the 12.7mm rifles were found very useful for hitting human targets at extreme ranges, but the weight of the weapon became a problem. As a result many military snipers switched to smaller rounds used by lighter rifles.
The calls for lighter rifles were loudest from snipers operating in Afghanistan, where U.S. Army and Marine Corps shooters wanted a lighter sniper rifle that could still consistently get kills out to 1,800 meters. The traditional 7.62mm round (for “standard” sniper rifles) was good only to about 800 meters. Soon several suitable rounds were found. The 300 Winchester magnum is a more powerful, but not much larger, round than the current 7.62mm one. By replacing the barrel and receiver of the $6,700 U.S. Army M24 sniper rifle, for about $4,000, you could fire the .300 Winchester Magnum round. This is longer (at 7.62 x 67mm) than the standard 7.62x51mm round and is good out to 1,200 meters. An improved version of the round extended that range another 200 meters or so.
There was another option, and that was to replace the barrel and receiver of the M24 sniper rifles to handle the .338 (8.6mm) Lapua Magnum round. Thus gave you a 7.7 kg (17 pound) sniper rifle and a round that could hit effectively out to about 1,600 meters. British snipers in Iraq, and especially Afghanistan, found the Lapua Magnum round did the job at twice the range of the standard 7.62x51mm round. The 8.6mm round entered use in the early 1990s, and became increasingly popular with police and military snipers. Dutch snipers used this round in Afghanistan with much success and already had a decade of experience with these larger caliber rifles. British snipers in Afghanistan soon adopted the 8.6mm round, having converted many of their 7.62mm sniper rifles. Recognizing the popularity of the 8.6mm round, Barrett, the pioneer in 12.7mm sniper rifles, came out with a seven kilogram (15.5 pound) version of its rifle chambered for the 8.6mm. But the U.S. preferred the even lighter .300 Winchester magnum solution.