Most of the numbers are the serial number.
Usually caliber and/or serial numbers.
All parts are stamped with the exact same serial number, indicating that they're all original to the rifle.
they can refer to year adopted, case length, bullet diameter, etc..
The grain numbers on ammunition are the projectiles weight in grains, at 7000 grains to a pound equals 437.5 grains to an ounce.
What is sightin-in a rifle mean?
Possilbe, but, unlikely.
The calibre is approximately .30 inches, and the -06 indicates the year it was adopted by the US military.
Serial numbers were not required until 1968.
The correct size of the bullet that fits the rifle.
Try the receiver
Look on the butt.
Serial numbers were not required before 1968