[svandamme]

a mil dot is usually calibrated for the maximum magnification, but either way, they suck on anything other then fixed 10X scopes for actual milling..and big known size targets
10x makes the formula easier, but hardly anyone but a military sniper will use mildots for milling anyway.

I took my 10x40 Mark4 leupold out to 1000 yards with great results in Bisley and a bit past that in Norway, and on known ranges you can use the mildots for overholding in wind rather then clicking windage.
Which for that MARK4 helped since it had .5 moa windage turrets.. and the overhold was much easier to do

You can use the dots on any magnification if you zero and mark down the drop vs the dots you have at that magnification..
It's just a question of getting used to your scope reticle for your range of distances and rifle ballistics.

Just shoot it a lot and take notes of each shot's conditions