Letter S

The Definition of Sectional Density

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Sectional Density

The relationship between a bullet's weight and its diameter. A long bullet, such as the original 7.62x54R loading for the Mosin Nagant 91/30, will have a high sectional density and consequently greater penetration than a shorter bullet of similar construction. A shorter bullet with less sectional density will have relatively less penetration, but greater knockdown power.


19 Other Firearms Definitions You Need To Know


Twist

The length, within a rifled barrel, required to accomplish one full rotation. 1:12 Twist, means a bullet passing down the bore would complete one revolution in twelve inches. 1:7 Twist, means a bullet passing down the bore would complete one revolution in seven inches, which makes it a tighter twist than 1:12. Different weights of bullet require appropriate rates of twist.

Headstamp

Markings impressed into the base of a cartridge case, normally identifying the maker's name, the cartridge calibre designation, and sometimes the date.

Recoil Operation

Recoil operation is an operating mechanism used in locked-breech, autoloading firearms. As the name implies, these actions use the force of recoil to provide energy to cycle the action.

Trace

Visible disturbance in the air by a bullet. Typically this takes the form of image distortion that persists for a fraction of a second in the shape of an inverted V similar to that of a boat wake.

WRF

Abbreviation for Winchester Rim Fire.

Bore Snake

A bore snake is a tool used to clean the inside (bore) of the barrel of a gun. It resembles a short section of rope with a smaller, weighted cord attached to one end to help feed the bore snake through the barrel. A bore snake often has one or more integrated brushes to help clean the barrel, and may also be used to apply lubricant. It is an alternative to using a cleaning rod and patches to clean the barrel of a gun. Bore snakes are made in different sizes for different calibers and gauges of guns.

Compensator

Also call a Muzzle Brake. A device attached to or made as part of a firearms barrel designed to reduce recoil or muzzle movement on firing. They generally increase muzzle blast.

Scattergun

A slang term for a shotgun.

Federal Firearms License

A Federal Firearms License (FFL) is a license in the United States that enables an individual or a company to engage in a business pertaining to the manufacture of firearms and ammunition or the interstate and intrastate sale of firearms. Holding an FFL to engage in certain such activities has been a legal requirement within the United States since the enactment of the Gun Control Act of 1968.

Mushroomed Bullet

A description of a bullet whose forward diameter has expanded after penetration.

Turk's Head

A tip for a cleaning rod, a jag, with spirally-radial wires for vigorously scrubbing a gun's bore.

Factory Ammo

Ammunition that has been assembled by a commercial vendor of ammunition and sold in retail stores. This is as opposed to Hand loads which have been assembled by individuals and are not typically sold.

LR

Abbreviation for Long Rifle. Typically used in the .22 caliber cartridge designation .22LR. However can be used as an abbreviation for Kentucky Long Rifle

Telescopic Sight

An optical sight, offering some magnification, often variable, with some kind of adjustable aiming grid inside (a reticle), which when mounted on a firearm, usually a rifle, makes sighting easier.

Scope

A magnifying tube through which the shooter may see the target and aim the firearm. Scopes contain a reticle, commonly in the shape of a cross, which must be properly centered upon the target for accurate aim.

Cast Off

An offset of a gun stock to the right, so that the line of sight aligns comfortably with the right eye while the butt of the stock rests comfortably on the right shoulder. Almost all right-handed shooters benefit from a little castoff and most custom built guns are made this way. The only question is how much. The castoff of a gun is about right when, with the gun comfortably mounted, the front bead lines up with the center of the standing breech.
A stock offset to the left, for shooting from the left shoulder is said to be

Polygonal Rifling

A type of gun barrel rifling where the traditional lands and grooves are replaced by "hills and valleys" in a rounded polygonal pattern, usually a hexagon or octagon. Polygons with a larger number of edges provide a better gas seal in relatively large diameter polygonally rifled bores.

Falling Block

A type of action used primarily for single shot rifles whereby some kind of lever actuates a breechblock, moving it downwards in a vertical recess to expose the chamber. May have visible or enclosed hammer. For any given barrel length, it allows a shorter overall rifle length compared to a bolt action because no space is taken up by the forward-and-back cycling of the bolt. Most of the better British makers produced them in limited numbers around the turn of the last century, the Farquharson being the most iconic. Perhaps the best-known falling block action today is the Ruger No.1.

Extractors

A part in a firearm that serves to remove brass cases of fired ammunition after the ammunition has been fired. When the gun's action cycles, the extractor lifts or removes the spent brass casing from the firing chamber.