Easy that's a bit of an aggressive tone, Lynx's comment was directed to my post, SWITCH TO THREADED
But yeah, the 5.56 is a weak round in that it's small and thus lacks stopping power (because it makes a nice wound and goes straight through the target)
The 7.76 or whatever, yes it is a heavier round, makes a bigger inpact and thus has more stopping power (like a shotgun) at the same time, it makes a nastier wound.
The 50. is heavily regulated, as it creates a wound that is largely impossible by a medic to tend, thus Geneva arn't fond of it. (The .50 is an anti vehicle round supposedly)
But yeah, 5.56 lacks power, but at the same time it's lightweight meaning you can carry more.
The 5.56 got introduced after ww2 when commanders found the larger rounds were "too" powerful, and if soldiers used a smaller round they could carry a lot more. If I got stuck in combat, I'd much rather have 200 rounds of 5.56 than 100 of 7...
Finally, a smaller round means a bigger clip. The G3A3 in BF2 fires a bigger round, thus it's magazine is only 20 rounds. There's advantages and disadvantages of all kinds of ammo.