Rifle Scope Glossary of Terms & Acronyms

ACOG: Advanced Combat Optical GunsightAO: Adjustable Objective. Parallax correcting feature located at the end of the scope (objective lens). 

BDC: Bullet Drop Compensation. A BDC scope compensates for the possible effects of gravity, wind conditions, etc, on the bullet’s trajectory.

Clicks: Number of times you will turn the turret when fine-tuning while zeroing your scope. 

Elevation: Vertical crosshair of the optic. 

Eye Relief: How far your eye should be from the rear lens (eyepiece) so the image is clear. 

Eyepiece Lens: This is the lens that is closest to your eye. It is also referred to as an Ocular Lens. 

FFP: First focal plane. The crosshairs in FFP scopes increase in size as magnification increases.

Field of View: Area that you can see through the scope at different magnification levels.  

IR: Illuminated Reticle. These reticles light up when turned on. It makes it easier to see if there is not enough ambient light. 

LPVO: Low Power Variable Optic. A scope where the magnification begins at 1x. 

LR: Long Range. 

MIL: Millradians of Angle. It is used to determine the elevation and windage adjustments. This measurement system is more often found in European optics. 

MOA: Minute of Angle. It is used to determine the elevation and windage adjustments. This measurement system is more often found in American optics. 

Ocular Lens: This is the lens that is closest to your eye. It is also referred to as an Eyepiece Lens. 

Objective Lens: This is the end of the scope that is flared.

Parallax: These adjustments allow you to clearly view the crosshairs and the target simultaneously. Without parallax adjustment, it is difficult to have a close object and a faraway object in focus simultaneously. This is mainly needed at higher magnifications. 

Picatinny: A rail system for mounting a scope to a rifle. 

POI: Point of Impact. This refers to your target or where you intend for the bullet to hit. 

Power: Magnification of the scope. If a scope is listed as 3-12x42mm, the magnification is 3x – 12x.

Reticle: The crosshairs of the scope. 

Rimfire: Where the firing pin strikes the bullet. 

RS: Rifle Scope. 

RTA: Rapid Target Acquisition

SFP: Second Focal Plane. With an SFP scope, the crosshairs remain the same size as magnification increases. 

SS: Sun Shade. It attaches to the rifle scope to provide shade from the sun when shooting. 

Subtension: Area of the target that is within the crosshair. 

Turrets: These are the knobs or dials on the scope that allow for adjustments in elevation and windage. 

Variable Power: The range of magnification for a scope. For a 3-12x42mm, the range of magnification is 3x – 12x. 

Weaver: Type of mount for a rifle scope. 

Windage: Horizontal crosshair of the optic. 

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