Letter S

The Definition of Sectional Density

Arsenal Exchange - Firearms Classifieds - Industry Directory

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


To tilt a gun to one side or the other, complicating sighting considerably. Can cause material loss of accuracy, particularly with a rifle at longer ranges. Some better long range target rifles are equipped with Spirit Level sights to help control canting.


Abbreviation for Federal Firearms [Dealer's] License.

Off Hand

To shoot while standing and without bracing against anything. Sometimes it can also mean to shoot with your non-dominant hand.


A railgun is an electrically powered electromagnetic projectile launcher based on similar principles to the homopolar motor.
Using a magnetic field powered by electricity, a rail gun can accelerate a projectile up to 52,493 feet (16,000 meters) per second.
A railgun consists of two parallel metal rails (hence the name) connected to an electrical power supply. When a conductive projectile is inserted between the rails (at the end connected to the power supply), it completes the circuit. Electrons flow from the negative terminal of the power supply up the negative rail, across the projectile, and down the positive rail, back to the power supply.


The portion of the stock (on a rifle) or frame (on a pistol) gripped by the trigger hand.

Cylindro Conoidal Bullet

A hollow base bullet, shaped so that, when fired, the bullet will expand and seal the bore. It was invented by Captain John Norton of the British 34th Regiment in 1832, after he examined the blow pipe arrows used by the natives in India and found that their base was formed of elastic locus pith, which by its expansion against the inner surface of the blow pipe prevented the escape of air past it.


The heading of a bullet, used in external ballistics that refers to how the Magnus effect causes bullets to move out of a straight line based on their spin.

Passive Safety

Any safety, internal or external, which functions apart from the shooter's conscious control. Grip safeties are one example of a passive external safety.

Firing Line

A line, either imaginary or marked, from which people shoot their firearms down range.


The original small single-shot or multi-barreled pocket pistol designed and manufactured by Henry Deringer of Philadelphia. Derringers (spelled with two Rs) are called that because of the original desinger and anmufactuturer of that type of gun, Henry Deringer. To get around copyright infringment other designers and manufacturers spell the name with two Rs. However guns designed and built by Deringer are spelled with only one R

Combination Gun

A shoulder-held firearm that has two barrels; one rifle barrel and one shotgun barrel. Most combination guns are of an over/under design (abbreviated as O/U), in which the two barrels are stacked vertically on top of each other, but some combination guns are of a side-by-side design (abbreviated as SxS), in which the two barrels sit beside each other.

Low Kneeling

A shooting position in which one or both knees are touching the ground and the shooter is as low as possible.


The speed at which a projectile travels. Velocity is usually measured in feet per second or metres per second.

Scout Rifle

A concept created by eminent gun writer Col. Jeff Cooper. A scout rifle, generally, is a bolt action carbine firing a medium power round suitable for taking large game (e.g., .308), fitted with a long eye-relief telescopic sight mounted on the barrel, and a back up set of iron sights.

Touch Hole

A small orifice at the breech end of the barrel of a muzzle-loading firearm through which the exploding priming charge is conducted from the flash pan to the main charge.

Recoil Compensator

A device fitted inside the buttstock of a heavily-recoiling gun or rifle, usually containing mercury and a valve. As the gun recoils, the mercury is displaced temporarily, increasing the duration, and thus diminishing the perceived impact of the recoil. The added half-pound of weight doesn#39;t hurt either.

Double Feed

A malfunction in which the spent case fails to eject from a semi-automatic firearm and blocks the chamber. As the fresh round is brought forward it cannot enter the chamber. It is cleared by stripping the magazine from the gun, racking the slide several times to eject the spent case, and then reloading.

Cold Clean Bore

The first shot from a rifle that has been cleaned, and not fired recently may go to a different point of impact, for the same point of aim than a rifle that has been fired recently. This first shot is referred to as a shot from a cold, clean, bore.

Funeral Grade

A colloquial term to describe a break-open gun, of any quality but often of the very highest, bearing the least possible decoration; having an all-blued receiver with either no engraving at all or only a simple borderline.