With only 10 MOA or 5 mils per turn, the Nightforce requires more than one turn of the knob to get past 500 yards.
The other thing long-range shooters have to specify is the windage correction, to compensate for wind drift or target movement. The same considerations apply here as for elevation, except that the
Long-range shooter Ray Sanchez dials the EREK knob on his USO SN-3 scope before engaging a long target with his G.A. Precision 7 mm WSM.
Fixed-power scopes such as the 10x Unertl and the original Leupold Mark 4 used to be the only serious contenders for military-spec sniper scopes due to durability. However, modern high-end variable magnification scopes have no problem with durability. At low magnification, they provide higher speed for close target engagements and more low-light capability. Illuminated reticles are a necessity for low-light shooting, and they are standard on high-end tactical scopes.
How much magnification do you need? The answer is less than you might think. The scope needs to provide a clear image of the target for a well-defined sight picture. With good glass, a 12x scope is more than sufficient for 1000-yard shooting. To test the theory, I dialed down my 3-12x50 mm Schmidt & Bender scope to 4x and was able to make hits on a 36-inch target at 1300 yards; it was enough to discern the target from the background. A lot of people think they need very high magnification to shoot at long range, however, as the magnification is increased, the field of view gets smaller and it is harder to find the target in the scope. Another problem at high power is that the size of the exit pupil shrinks, which makes eye position a lot more critical for a full view through the scope. A smaller exit pupil also makes it harder to track the target though
Along with a solid rifle, accurate ammunition, range-finder, and data-book, a scope with the right features is key to making long-range hits.
For practical shooting to about 1000 yards, a top end of 12x to 16x gets the job done and puts the low end between 3x and 5x for most scopes. Another reason to pick the lowest magnification that will work for the longest shots is to help limit rifle weight and bulk. I regularly shoot scopes with maximum magnification of 12x, 15x, and 25x, and I have found that on the bigger models, I typically dial them down to the 12-15x range to shoot. With clear glass and a good reticle, a 12x scope is usable as far as 1350 yards on practical targets.
Many balk at spending $1000, not to mention almost $3000, on a rifle scope. This is somewhat misguided. While you consume ammunition, barrels, calories, and vehicle fuel in training and practice, the scope, rifle action, and stock are essentially fixed costs. The cost of the consumables will eclipse the fixed costs in just a year or two, while an optic that provides clear and bright images while being boringly dependable will pay off every time you pull the trigger.