Jose wrote:
.30/06 is the rifle caliber.

Nope.
.30-'06

Yep, caliber and year, not a fraction.


Ok, what do the numbers mean? I've heard of a "thirty ought six"
referring to a gun, and think I know one of them (.30 inches?) refers to
the gauge (width of the bullet). What's the other?

Short-hand for 1906, the year it was adopted.

http://www.gmdr.com/lever/3006stext.htm