NRA Sight Systems & Optics Flashcards

What term describes the proper relationship between the front sight post and the rear sight notch when they are correctly aligned for aiming?

Answer: Sight alignment

Sight alignment refers to the correct positioning of the front sight within the rear sight notch, which is a prerequisite for accurate shooting.

Which type of iron sight uses a circular rear aperture through which the shooter looks to align with the front sight?

Answer: Peep (aperture) sight

A peep or aperture sight uses a circular hole as the rear sight element; the eye naturally centers the front sight in the aperture for consistent alignment.

What is 'sight radius' on a firearm?

Answer: The distance between the front and rear sights

Sight radius is the measured distance between the front and rear sights; a longer radius reduces angular aiming error and generally improves practical accuracy.

Which sight technology gathers and concentrates ambient light through an optical polymer rod to produce a bright aiming dot?

Answer: Fiber optic sight

Fiber optic sights use a polymer optical fiber to collect surrounding light and concentrate it at the tip, creating a bright, high-visibility aiming point in daylight conditions.

In the context of firearm sights and ballistics, what does the abbreviation 'MOA' stand for?

Answer: Minute of Angle

MOA stands for Minute of Angle, an angular unit approximately equal to 1.047 inches at 100 yards, universally used to express sight adjustments and group sizes.

Which self-luminous sight type uses sealed vials of tritium gas to provide illumination in low-light and no-light conditions without batteries?

Answer: Tritium night sight

Tritium night sights contain small borosilicate glass vials filled with tritium gas, which emits light through radioluminescence and requires no external power source.

A 'ghost ring' rear sight is best described as which of the following?

Answer: A large-diameter, thin-walled rear aperture that visually fades during focus

A ghost ring sight features an oversized, very thin rear aperture; because the ring is thin and large, the shooter's eye naturally ignores it (it 'ghosts') while focusing on the front sight and target, enabling fast acquisition.

A rifle scope marked '3-9x40' indicates which combination of specifications?

Answer: 3 to 9 power variable magnification, 40mm objective lens diameter

In standard scope notation, the numbers before 'x' indicate the magnification range (3× to 9×), and the number after 'x' is the objective lens diameter in millimeters (40mm).

What is 'eye relief' as it applies to rifle scopes?

Answer: The distance between the eyepiece and the shooter's eye that produces a full, clear field of view

Eye relief is the specific distance the shooter's eye must be from the ocular lens to see the full sight picture; insufficient eye relief can result in scope bite (injury from recoil).

In a first focal plane (FFP) variable scope, how does the reticle behave when magnification is changed?

Answer: The reticle grows and shrinks proportionally with changes in magnification

A first focal plane reticle is placed before the magnification erector system, so it scales with the image — its subtensions remain calibrated and accurate at every power setting.

What is parallax error in a rifle scope, and when does it occur?

Answer: The apparent movement of the reticle relative to the target when the shooter's eye moves off the optical axis

Parallax error occurs when the target image and reticle are focused on different planes inside the scope, causing the reticle to appear to shift relative to the target as the shooter's eye position changes.

What is the function of a rifle scope's windage adjustment turret?

Answer: To move the reticle or impact point horizontally left or right

The windage turret moves the scope's reticle (and thus the point of impact) horizontally, allowing the shooter to correct for left or right deviations caused by wind or mechanical offset.

What does 'BDC' designate when describing rifle scope reticles?

Answer: Ballistic Drop Compensator

A BDC (Ballistic Drop Compensator) reticle features multiple holdover aiming points below the main crosshair, calibrated to correspond to bullet drop at progressively greater distances.

Which standardized military rail specification (MIL-STD-1913) provides uniform cross-slots for mounting scopes and accessories on firearms?

Answer: Picatinny rail

The Picatinny rail (MIL-STD-1913) features precisely spaced, uniform cross-slots that allow any compliant ring or accessory to be mounted, repositioned, and interchanged with consistent retention.

What is the correct procedure for zeroing a rifle scope at 100 yards?

Answer: Firing test groups and adjusting windage/elevation until the point of impact consistently matches point of aim at 100 yards

Zeroing requires firing live ammunition at a target and making incremental windage and elevation adjustments until the group center aligns with the intended aiming point at the specified distance.

What is the recommended method to verify a scope's reticle is properly leveled during installation?

Answer: Using a scope leveling kit with dual bubble levels on the action and scope

A scope leveling kit places a reference level on the receiver and a second level on the scope turret, ensuring the reticle is perfectly vertical and perpendicular to the bore axis to prevent canting errors.

What torque range is most commonly recommended for scope ring cap screws to ensure secure retention without damaging the scope tube?

Answer: 15–18 inch-pounds

Most scope and mount manufacturers specify 15–18 inch-pounds for ring cap screws, providing sufficient clamping force to resist recoil while avoiding crushing or deforming the scope tube.

What is the primary aiming advantage of a red dot (reflex) sight compared to traditional iron sights?

Answer: Faster target acquisition with both eyes open, requiring only a single focal plane

Red dot sights project an illuminated dot onto the same focal plane as the target, allowing the shooter to aim with both eyes open without aligning multiple sight components, dramatically speeding target acquisition.

What is the purpose of lapping scope rings before mounting a scope?

Answer: Removing material to ensure the ring bores are concentric and provide full, even contact with the scope tube

Lapping uses an abrasive rod to align and true the ring bore surfaces so they make full, uniform contact with the scope tube, distributing clamping force evenly and preventing stress points that could damage the scope or shift zero.

What is the function of a cantilever scope mount on an AR-15 flat-top receiver?

Answer: To extend the scope forward along the rail to achieve proper eye relief distance

On an AR-15, mounting a scope directly over the receiver often places the ocular lens too close to the shooter's eye; a cantilever mount moves the scope forward on the rail to achieve the correct eye relief distance.