Back during the second world war we had a menagerie of cartridge and guns available for the military. Every country had proprietary cartridge though a lot of gun designs were based on Mauser designs. Surprisingly they all were similar in performance. Not much difference between the 30-06 of US design, the 7.9 x 57mm Mauser, 303 British, 7.62 x 54R Russian or the Japanese 7.7 mm were all similar in performance but non-interchangeable.
Preferred Weapons After the Cold War
After the war the cold war divided the world. Eastern European powers formed the Warsaw Pact and settled on the 7.62 x 54R as their full power round, the 9 x 18 Makarov for sidearm and submachine guns. They also adopted the famous or infamous 7.62 x 39 mm that was chambered in the prolific AK-47 and SKS designs. The western countries formed NATO, the North Atlantic Treaty Organization, that included the western European countries and the US. In the pacific we have SEATO, The South East Asia Treaty Organizations. But standards where driven by NATO. The US developed 7.62 x 51 NATO became the standard full power rifle and machinegun round. The intermediate round was 5.56 x 45mm round fired by the M-16 and others like the M-4 and the 19th century 9 x 19mm for submachine guns and sidearms. The supply lines were thus streamlined so the PACT and NATO ammunition were standardized within the organizations. As an aside the western and NATO also standardized the 12.7 x 99mm Browning Heavy Machinegun cartridge. Used also for long range interdiction and precision long range shooting it is the premier long-range snipping caliber. While the Russians had the 12.7x108mm heavy machinegun round and is used in similar situation to the US version.
Level Playing Field Among World’s Military
When comparing specs, it would seem that all the major players are very similar. Many think that the 7.62 x 39mm is superior to the AK-74’s 5.45 x 39mm introduced in the 1970’s. Essentially the worlds military is a level playing field as far as rifles, machineguns and sidearms go. The 7.62 x 51mm NATO being a rimless round it is much easier to design semi-automatic rifles and full automatic machineguns verses the rimmed Russian round. Other that that stipulation all performance evaluations are roughly equal. The 7.62x54R pushes a 174-grain bullet to 2,610 fps, while the 7.62×51 NATO delivers a 175-grain bullet at muzzle velocity of 2,600-fps. On the receiving end the 10-fps difference isn’t going to matter. The specs for the Russian versus NATO intermediate range weapons are similar: 5.45×39 mm 57-grain with a muzzle velocity of 2,900 fps. Whereas the NATO round is a 62-grain bullet at about 3,150 fps. The difference at typical combat range and circumstances is negligible. The difference in sidearms and submachineguns is moot. The Russian Federation has recently standardized on the 9x19mm Luger or Parabellum round, same as NATO. The world has followed, except for China that has adopted the 5.8x42mm intermediate cartridge. The US is considering adopting the 6.8x43mm as the performance of the 5.56x45mm seems to be wanting in the short-barreled M-4 carbine. So, with the noted exceptions we are all, performance wise at least, on the same page.