Can you elaborate on this? Everyone I know has been citing the UK
Honestly, a lot of the UK stuff seems to almost have more in common with US gun owner culture than their anti-gun campaigners, though obviously organisations like the NRA would not be happy at all with UK levels of gun ownership restrictions. The fact that self-defence is not a valid reason to have a gun or any other weapon here would also be unacceptable to pretty much everyone in the US from what I can tell, not to mention unconstitutional. (This includes stuff like pepper spray.)
You're pretty close. Those rounds are measured in millimeters instead of caliber, so they should be 7.62mm (really 7.62x39mm or 7.62x51mm) and 5.56mm. The equivalent in calibers is .30 and .223. Notably, .223 is also an actual round and some rifles can fire either .223 or 5.56 (iirc, the cartridges are the same dimensions, but the pressure ratings are different).
AR-15's are typically chambered in 5.56mm. An AR style rifle chambered in 7.62x51mm would be an AR-10. Although you can get AR platform rifles chambered in pretty much whatever you want, going all the way up to .50 BMG. It's pretty uncommon to see anything like that, though.
Where does this strawman come from? Can you imagine the negative publicity if celebrity's bodyguard shot and killed someone? How often do you think celebrities are assaulted by attackers armed with guns?