This is a variation of the dangerous game theme, except that the intended quarry is human. In military and LEO applications, the operators may have to approach the target area from a distance in vehicles or dismounted, and may encounter threats along the way. The mission often requires operators to enter a building and clear it by either engaging or capturing occupants.
The preferred weapon sight for close quarters battle is either an iron sight or an optical reflex (aka “red dot sight”) or holographic sight. The optical reflex type of sight projects an image of the aiming reticle toward the shooter, with a focus at infinity. These sights allow the shooter to perceive an aiming dot or reticle as long as the eye pupil falls within the exit pupil of the sight. This greatly relaxes the need to align the eye with the aiming sight, and allows for rapid target acquisition at short ranges. It also allows the operator to easily aim the weapon using both eyes open. As there is no magnification and no minimum focus range with these sights, they are often referred to as having “0 magnification.” Preferably the iron sights are co-witnessed near the bottom portion of the optical sight or holographic exit pupil so that they can be used as a back-up without delay if the optical sight fails.
To enable more accurate long range shots, these sights are sometimes combined with a simple 3X-4X magnifying afocal telescope that is located between the shooter and the reflex sight. The magnifier is mounted on a pivoting hinge that allows the shooter to swing the magnifier out of the weapon sight optical path when it’s not needed. However, the magnifier is still attached to the rifle in this position and thus becomes a bulky appendage on the side of the receiver that can hinder operation in some shooting positions.
Another option is to use a variable magnification telescopic sight that has a low magnification of about 1X. Any telescopic sight is a compromise for close quarters battle (CQB). A few options exist for CQB/patrol, but any solution will be a compromise in some way. Because the front sight is not in focus, the scope must be removed to use the back-up irons. Military/LEO operators tend to prefer short-barreled (11-14.5”) fully automatic carbines. In this case, a short, lightweight scope would be highly preferred. While a lower magnification range of 1X is preferred for CQB for aiming with both eyes open, 1.1-1.5X is sometimes used. The Advanced Combat Optical Gunsight (ACOG) weapon sight has a fixed magnification between 1.5X and 6X and has become a popular compromise sight for CQB/patrol applications. With the right reticle and training, these higher magnification telescopes can be used with both eyes open.
These scopes are usually used with an automatic or semi-automatic carbine rifle chambered in 5.56×45. Other chamberings such as 6.8 SPC, 7.62×39 and 7.62×51 are sometimes used. During patrol, target ranges up to 250 yds or more can be encountered. A ballistic drop compensated reticle is sometimes used to improve aiming accuracy for long range shots. These reticles tend to be complicated and can obstruct the field of view during CQB. Illuminated reticles should be compatible with night vision goggles, which means they should be very dim on the lowest intensity setting. A wide field of view, low image distortion, and a clean, uncluttered sight picture are high priorities. Glare performance and off-axis aberration correction are not important for low magnification ranges.
However, magnifications as high as 8X are useful in target identification. Recently, 1-8X scopes have been introduced for this purpose. There are three limitations to these products. 1) In general, the exit pupil is not as large at 1X as it is for a comparable quality 1-4X variable scope. The smaller exit pupil can hinder target acquisition speed. 2) These scopes typically have a compact 24mm obective, providing a small 3mm exit pupil. This exit pupil is adequate for daytime use. In low light, however, this exit pupil will be smaller than the eye pupil, resulting in a low brightness image. 3) At 8X glare performance starts to become an issue in these scopes. The use of a sun shield is not really an option for a carbine or a wide field of view (1X setting). If you need a 1-8X magnification range, glare performance will be a priority and the choice in scopes is limited. Expect to pay a high premium for such a large magnification range.