The AR15 or M16 zero's at 25 meters, not yards. The 25 meter zero is also the 300 meter zero. In high power competition shooting, you'll zero your AR at 200 yards, then get a zero for 300 yards and 600 yards. You'll figure out these three zeros and will write them in your log book, so you'll know how many clicks it's going to take to hit the 10 ring the first time out at the different firing lines. If you use a M1A for high power competition, you'll shoot to find these three same zeros for your rifle.
The military always uses meters now and civilians always use yards it seems.
As for .308 and .30-06, they are usually zeroed at 200 yards or 200 meters, depending on which you want to use. Most .308 battle rifles, like the fal, start their rear sights at 200 yards, as in the L1A1, or at 200 meters at in the G1 FAL. For M1 Garands, most find their zeros for each 100 yards, then mark it down in a log book. You might even find some rifleman that place marks on their rear sights to where certain zeros are.
And with a lot of bullet drop compensated scopes, you'll zero at 200 yards or meters.
Leading to, if you really want to find out where your rifle shoots, write your shots down in a log book with where the sights are set at.