My rifle is sighted in at 200 when the rear sight is bottomed out.
That way its easier to quickly return to zero.
I do a lot of practice at 100 on the NRA reduced targets. Using my 200 yard zero (bottomed out) I'm on at 100 if I turn the front sight UP one full revolution.
Then, when I move to 1000 from 600, I leave the rear sight alone and turn the front sight down 4 full revolutions.
Depending on the enviormental conditions (light, temp, etc) I use the rear sight to fine tune it.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071