There are many variations of the 7.62 cartridge. The 7.62mm cartridge has been used in many weapons known to world history. The following rounds are based on 7.62mm:

• 7.62x25
• 7.62x54R
• 7.62x51
• .308
• 7.62x39
• 7.62x54R

Some of these were more popular than others, and were used in both pistols and rifles. Some of these cartridge are still in heavy use. Over time, the 7.62 round proved to be a cheap, reliable, and effective.

Back to the original question, the 7.62mm (.30 caliber) was initially declared a NATO standard. The NATO standard was based on industrial efficiency. The same machines, tools, and gauges could be used to produce components used in different guns. Things like barrels, parts, and ammo could all be produced without having to re-machine a factory.

In addition, NATO countries could easily trade supplies without having to retrain troops or acquire additional supplies needed to accommodate weapons based on a 7.62mm cartridge.