[FirstFreedom]

Caliber is measured in 100ths of an inch... thru the maximum diameter of the bullet.

Yes, actual bullet diameter, which corresponds to barrel/bore groove diameter. And well, sometimes it's measured in 100ths of an inch; sometimes (more often) it's measured in 1,000ths of an inch.

Metric bullets are measured in millimeters...thru the maximum diameter...

No I do not believe so, if by "thru the maximum diameter", you mean the absolute max bullet actual diameter. Instead of measuring actual bullet or groove diameter,the metric designations measure the smaller LAND diameter of the bore. For example a .308 bullet measures 7.82mm, NOT 7.62mm, so using the metric/european convention, it's named in millimeters with the smaller one (7.62mm), not the actual bullet diameter (7.82). This holds true again and again and again, if you start running the numbers on metric named rounds. The difference is nearly always the same: The metric name is between 8/1,000ths" and 11/1,000ths" smaller than the actual bullet diameter. The 0.20 mm is right in this range of about 10/1,000ths (or 1/100th) of a difference, in the case of 7.62x51mm.

Then yes, you have the many anamolies of american-named cartridges which, for marketing reasons, the name is a larger diameter than the actual bullet:

-".44 mag" and ".44 spec" are .429
-".38 special is .357/.358
-".454 casull" is .451/.452
-".460 rowland" is .451/.452
-".460 s&w mag" is .451/.452

and on and on.