Firearms Glossary
Comprehensive dictionary of firearms terminology with 120 terms.
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+
+P Plus P
Ammunition loaded to higher pressure than standard, producing higher velocity. Verify firearm is rated for +P.
+P+ Plus P Plus
Ammunition loaded to even higher pressure than +P. Use only in firearms specifically rated.
A
Absolute Co-Witness
Iron sights align in the center of the optic's window.
Action
The mechanism that loads, fires, and ejects cartridges.
AOW Any Other Weapon
NFA category for certain unusual firearms like pen guns or smooth-bore pistols.
ATF Bureau of Alcohol, Tobacco, Firearms and Explosives
Federal agency regulating firearms.
Automatic Full-Auto
Continues firing as long as the trigger is held and ammunition remains. Heavily regulated (NFA).
B
Barrel
The metal tube through which the bullet travels. Rifling imparts spin for stability.
BC Ballistic Coefficient
A measure of a bullet's ability to overcome air resistance. Higher BC = better long-range performance.
BCG Bolt Carrier Group
The assembly in semi-auto rifles that chambers rounds, fires, extracts, and ejects casings.
BDC Bullet Drop Compensator
A reticle with markings for holdover at various distances.
Blowback
Operating system where expanding gases push the bolt/slide rearward.
Bolt Action
Manually operated action where the shooter cycles the bolt to chamber rounds.
Bore
The interior of the barrel through which the bullet passes.
Break Action
Action where the barrel(s) pivot away from the receiver for loading.
Bullet Drop
The vertical distance a bullet falls below the line of bore due to gravity.
Buttstock
The rear portion of the stock that contacts the shooter's shoulder.
C
CCW Carrying a Concealed Weapon
Permit/license to carry a concealed firearm.
Centerfire
Ammunition with the primer located in the center of the cartridge base.
Chamber
The portion of the barrel where the cartridge sits before firing.
Cheek Weld
Consistent placement of the cheek against the stock for proper sight alignment.
Clip
A device that holds cartridges together for loading into a magazine. Often incorrectly used to mean magazine.
Co-Witness
Alignment of iron sights with an optic, allowing use of either sighting system.
Compensator
Muzzle device that redirects gases upward to reduce muzzle rise.
Constitutional Carry
State law allowing concealed carry without a permit.
CWP Concealed Weapon Permit
Same as CCW - state-issued permit for concealed carry.
D
DA/SA Double Action/Single Action
First shot is double action, subsequent shots are single action.
DAO Double Action Only
Every trigger pull is double action. Common in some defensive pistols.
DD Destructive Device
NFA category for explosives and firearms over .50 caliber (with exceptions).
DI Direct Impingement
Gas system where gas is routed directly to the bolt carrier.
DOPE Data On Previous Engagement
Recorded data of elevation and windage adjustments for various distances.
Double Action DA
Trigger both cocks and releases the hammer/striker in one pull.
E
Elevation
Vertical adjustment on sights to compensate for bullet drop at various distances.
Eye Box
The three-dimensional space behind the scope where the shooter can see the full field of view.
Eye Relief
The distance from the eyepiece to your eye where the full image is visible. Critical for safety with recoiling firearms.
F
FFL Federal Firearms License
License required to engage in the business of selling firearms.
FFP First Focal Plane
Reticle placement where the reticle size changes with magnification. Holdovers accurate at all magnifications.
Flash Hider
Device that disperses muzzle flash to reduce visibility to the shooter.
Flinch
Involuntary anticipation of recoil causing movement before the shot.
FMJ Full Metal Jacket
A bullet with a soft core encased in a shell of harder metal, preventing expansion on impact.
Follow Through
Maintaining sight picture and trigger control after the shot breaks.
Form 1
ATF form to manufacture an NFA item (e.g., building an SBR).
Form 4
ATF form for transferring an NFA item to an individual or trust.
Form 4473
ATF form completed when purchasing a firearm from an FFL for background check.
FPS Feet Per Second
Unit of measurement for bullet velocity.
G
Gas Operated
System using gas tapped from the barrel to cycle the action.
GCA Gun Control Act
1968 law establishing the FFL system and prohibited persons categories.
Grain gr
Unit of weight measurement for bullets and powder. 7,000 grains = 1 pound.
Group
A cluster of bullet holes on a target from multiple shots.
Grouping
The measure of how close together shots land on target.
H
Hammer
A pivoting component that strikes the firing pin when released by the trigger.
Handguard
The portion of the firearm surrounding the barrel that protects the shooter's hand from heat.
Hold Over
Aiming above the target to compensate for bullet drop.
Hold Under
Aiming below the target when shooting at closer ranges than zero.
Holographic Sight
Uses laser-generated hologram to create a reticle image. Functions even if lens is damaged.
J
JHP Jacketed Hollow Point
A bullet with a hollow cavity designed to expand upon impact, increasing stopping power.
K
Kentucky Windage
Aiming off-target to compensate for wind without adjusting sights.
KeyMod
A modular mounting system using keyhole-shaped slots.
L
Lever Action
Action cycled by a lever, typically located around the trigger guard.
Lower 1/3 Co-Witness
Iron sights visible in the lower third of the optic's window.
Lower Receiver
On AR-style rifles, the serialized portion containing the trigger group and magazine well.
LPVO Low Power Variable Optic
Variable magnification scope starting at 1x, combining red dot speed with scope precision.
LTC License to Carry
Term used in some states for concealed carry permit.
M
M-LOK
A modular accessory mounting system using slots and locking lugs.
Magazine
A detachable container holding ammunition that feeds into the firearm.
MIL Milliradian
Angular measurement equal to 3.6 inches at 100 yards. Common in tactical scopes.
MOA Minute of Angle
Angular measurement equal to 1.047 inches at 100 yards. Used for scope adjustments and accuracy measurement.
MRAD Milliradian
Same as MIL - angular measurement used in precision shooting.
Muzzle
The end of the barrel where the bullet exits.
Muzzle Brake
Device attached to the muzzle that redirects gases to reduce felt recoil.
Muzzle Energy
The kinetic energy of a bullet as it leaves the barrel, measured in foot-pounds (ft-lbs).
Muzzle Velocity
The speed of a bullet as it leaves the barrel, measured in feet per second (fps).
N
Natural Point of Aim NPA
The direction your body naturally points when in shooting position.
NFA National Firearms Act
1934 law regulating machine guns, suppressors, SBRs, SBSs, AOWs, and destructive devices.
NICS National Instant Criminal Background Check System
FBI system used for firearms purchase background checks.
O
Open Carry
Carrying a firearm visibly in public.
P
Parallax
The apparent movement of the reticle relative to the target when the shooter's eye moves. Adjustable on precision scopes.
Pistol Brace
Stabilizing device for AR-style pistols. Subject to ATF regulations.
Pistol Grip
A grip that allows the hand to hold the firearm at an angle similar to holding a pistol.
Piston Gas Piston
Gas system using a piston to drive the bolt carrier.
Point of Aim POA
Where the sights are aligned on the target.
Point of Impact POI
Where the bullet actually strikes.
Primer
The component in a cartridge that ignites when struck by the firing pin, igniting the powder charge.
Private Sale
Firearm sale between private individuals, not involving an FFL.
Prohibited Person
Individual legally barred from possessing firearms (felons, domestic violence, etc.).
Pump Action
Action cycled by sliding a forend back and forth. Common in shotguns.
R
Rail Picatinny Rail
A mounting platform with standardized slots for attaching accessories.
Receiver
The main body of a firearm that houses the operating parts. Legally considered the 'firearm.'
Red Dot
Non-magnifying optic that projects an illuminated dot onto the lens for fast target acquisition.
Revolver
Handgun with a rotating cylinder containing multiple chambers.
Rifling
Spiral grooves cut into the barrel bore that spin the bullet for accuracy and stability.
Rimfire
Ammunition where the primer is located in the rim of the cartridge base (e.g., .22 LR).
S
Safety
A mechanism that prevents the firearm from firing when engaged.
SAO Single Action Only
Requires manual cocking before each shot (e.g., 1911).
SBR Short Barreled Rifle
Rifle with barrel under 16" or overall length under 26". NFA regulated.
SBS Short Barreled Shotgun
Shotgun with barrel under 18" or overall length under 26". NFA regulated.
Semi-Automatic Semi-Auto
Fires one round per trigger pull, automatically chambering the next round.
SFP Second Focal Plane
Reticle placement where the reticle stays the same size. Holdovers only accurate at one magnification.
Sight Alignment
The proper relationship between the front and rear sights.
Sight Picture
The visual alignment of the sights with the target.
Single Action SA
Trigger only releases the hammer/striker. Must be manually cocked first.
SOT Special Occupational Tax
Tax paid by FFLs to deal in NFA items.
Stock
The part of a long gun that braces against the shoulder.
Straw Purchase
Illegal purchase of a firearm on behalf of someone who cannot legally buy one.
Striker
A spring-loaded firing pin that strikes the primer when released by the trigger.
Striker-Fired
Action using a spring-loaded striker instead of a hammer.
Sub-MOA
Accuracy capable of shooting groups under 1 MOA (1.047" at 100 yards).
Subsonic
Ammunition with velocity below the speed of sound (~1,125 fps), often used with suppressors.
Supersonic
Ammunition with velocity above the speed of sound, creating a sonic crack.
Suppressor Silencer
Device that reduces the sound and flash of a firearm. NFA regulated item.
T
Trajectory
The curved path a bullet travels from the muzzle to the target due to gravity.
Trigger
The lever pulled by the finger to fire the weapon.
Trigger Control
Proper technique for pressing the trigger without disturbing aim.
Trigger Pull
The amount of force required to release the striker or hammer.
Trigger Slap
Jerking or slapping the trigger, causing accuracy issues.
Twist Rate
The rate of spin imparted by rifling, expressed as 1:X (one rotation per X inches).
U
Universal Background Check
Requirement for background checks on all firearm transfers including private sales.
Upper Receiver
On AR-style rifles, the portion containing the barrel, bolt carrier group, and charging handle.
W
Windage
Horizontal adjustment on sights to compensate for wind drift or zero the firearm.
Z
Zero
The point of aim equals the point of impact at a specific distance.