As I recall, one of the primary motivations for switching to 5.56 NATO was that you could carry roughly twice as much for the same weight as you could 7.62 NATO. Full-on 7.62 NATO battle rifles are also very hard on the troops using them, I've heard them described as "fully-automatic flashbangs", with deleterious effects on situational awareness due to the power of the round.

Given that most countries wanted to switch away from 7.62 anyway - it's a round fit for combat out to 600+ metres, which, given the amount of fire support most infantry has on tap, is kinda pointless - 5.56 was a decent enough fit, but, perhaps more importantly, it was an American-produced cartridge. The British .280 (7mm) was also up for consideration but the US effectively vetoed it.

And oh, look. The next calibre the US is after is 6.8mm. Not that I expected them to actually choose a 7mm round, that would be a little too on the nose.

As I recall, one of the primary motivations for switching to 5.56 NATO was that you could carry roughly twice as much for the same weight as you could 7.62 NATO. Full-on 7.62 NATO battle rifles are also very hard on the troops using them, I've heard them described as "fully-automatic flashbangs", with deleterious effects on situational awareness due to the power of the round.

Given that most countries wanted to switch away from 7.62 anyway - it's a round fit for combat out to 600+ metres, which, given the amount of fire support most infantry has on tap, is kinda pointless - 5.56 was a decent enough fit, but, perhaps more importantly, it was an American-produced cartridge. The British .280 (7mm) was also up for consideration but the US effectively vetoed it.