About NATO milliradians
One NATO mil is 1/6,400th of a circle, or 0.05625°, so a degree is about 17.78 NATO mils.
A NATO mil is close enough to a true milliradian (6,283 of those make a circle) that gunners treat it as 1 meter of width at 1,000 meters of range. A circle of 6,400 also divides neatly into quarters, eighths and sixteenths.
About USSR milliradians
The USSR mil was the angle unit of Soviet artillery. It is a rounded version of the milliradian, within a few percent of one thousandth of a radian.
Soviet artillery used the mil in its sights and for estimating range: a target of known width that covers a measured number of mils gives the distance.
Like the other mils it is a military convention rather than an SI unit – each army chose a convenient number of divisions for the circle, so check which mil a figure refers to.
There are 6,000 USSR milliradians to a full circle.