The newest adaptive rifles, such as the Remington ACR and Cz. 803, can fire both 5.56x45 and 7.62x39 with a quick barrel change and bolt face change. The Cz. 803 goes one step further, and even has a modular magazine well.
762 mm
2.5 feet = 762 mm
Yes there is a difference. They are physically the same size casing, but the 556 military rounds' chamber pressure is ~10,000 psi higher then 223. Military rifles generally have chambers with a different throat configuration than normal sport 223 rifles. This being said, I would not recommend shooting 556 unless your rifle was designed for the higher pressures.
762 mm
0.762meters
There are 10 mm in a cm, and 2.54 cm in an inch. Therefore, 7.62 mm equals .762 cm and .762 cm equals .3 inches. The answer is .3
76.2 cm
76.2 cm = 762 mm
30 mm = 1.18 inches (rounded)Direct Conversion Formula 30 mm*1 in25.4 mm=1.181102362 in
1013 millibar or 762 mm of Mercury
78x30 inches
2.5 feet = 762 millimeters.