How important are caliber markings?

[jumbopanda]

Exactly how important are a gun's caliber markings? Do they bear any legal significance like a serial number? Would it be illegal to have a gun with incorrect caliber markings, say you stick a 6.8mm upper on a AR-15 lower that's marked as .223/5.56. Or if you removed the markings? :confused:

[blkA4alb]

Exactly how important are a gun's caliber markings? Do they bear any legal significance like a serial number? Would it be illegal to have a gun with incorrect caliber markings, say you stick a 6.8mm upper on a AR-15 lower that's marked as .223/5.56. Or if you removed the markings? :confused:
The markings mean nothing. Hell some receivers are marked Multi for the caliber.

[bwiese]

Caliber is supplementary information.

The only time it might be important is for .22LR ARs if there's an open magwell.