While the long distance 50 caliber sniper rifles can kill at 8,000 yards.
At over a mile away you have a full seven seconds from the time between squeezing off the first round and the terrorist hearing the first bullet!
That’s enough time for three shots before the ememy hears you!
However, you can also mount a high-powered rifle scope on an AR-15 or M-4 for high-speed shooting at up to 400 yards.
When mounting a rifle scope on an AR15, resist the temptation to stack AR-15 rifle sights because you lose cheek weld, vital for long distance kills.
Don’t do this!
Instead, get a quick release for a picatinny rail and mount the telescopic sight as close to the AR barrel as possible:
Use a quick release rail to allow you to use your battle sights also
Note that the telescopic sight blocks the charging handle.
You also need to add an AR-15 Charging Handle Assembly extender to allow you to load the weapon.
Use a charging handle adapter to get around the rifle scope