NRA NRA Sight Systems & Optics 2 — Questions and Answers
Question 1: A rifle scope marked '3-9x40' indicates which combination of specifications?
- 3 to 9 meter effective range, 40mm tube diameter
- 3 to 9 power variable magnification, 40mm objective lens diameter (Correct answer)
- 3 to 9 MOA adjustment range, 40mm eye relief distance
- 3 to 9 inch click value, 40mm ocular lens diameter
Correct 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).
Question 2: What is 'eye relief' as it applies to rifle scopes?
- The range of magnification adjustment available on a variable scope
- The diameter of the ocular (eyepiece) lens in millimeters
- The distance between the eyepiece and the shooter's eye that produces a full, clear field of view (Correct answer)
- The amount of reticle adjustment available from center
Correct 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).
Question 3: In a first focal plane (FFP) variable scope, how does the reticle behave when magnification is changed?
- The reticle remains the same apparent size at all magnification settings
- The reticle shifts laterally to track bullet drop compensation
- The reticle grows and shrinks proportionally with changes in magnification (Correct answer)
- The reticle illumination automatically adjusts with magnification
Correct 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.
Question 4: What is parallax error in a rifle scope, and when does it occur?
- Chromatic lens distortion that blurs the target image at high magnification
- The apparent movement of the reticle relative to the target when the shooter's eye moves off the optical axis (Correct answer)
- Vertical drift of the point of impact caused by barrel heating
- Mechanical backlash in the windage or elevation turrets
Correct 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.
Question 5: What is the function of a rifle scope's windage adjustment turret?
- To change the focal plane of the objective lens for parallax correction
- To adjust the elevation of the reticle for bullet drop compensation
- To move the reticle or impact point horizontally left or right (Correct answer)
- To control the illumination brightness of an illuminated reticle
Correct 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.
Question 6: What does 'BDC' designate when describing rifle scope reticles?
- Base Distance Calibration
- Barrel Diameter Correction
- Ballistic Drop Compensator (Correct answer)
- Binocular Diopter Control
Correct 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.
Question 7: Which standardized military rail specification (MIL-STD-1913) provides uniform cross-slots for mounting scopes and accessories on firearms?
- Dovetail rail
- Weaver rail
- Picatinny rail (Correct answer)
- Tip-off rail
Correct 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.
NRA NRA Sight Systems & Optics 2
A rifle scope marked '3-9x40' indicates which combination of specifications?