Letter D Firearms Glossary

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DA/SA

Abbreviation for Double Action/Single Action. A type of firearm that is designed to operate in double action on the first shot, and in single action on the second and subsequent shots.

Damascus Barrels

Barrel tubes built up by twisting alternate strips of iron and steel around a fixed rod (mandrel) and forge-welding them together in varying combinations according to the intended quality and the skill of the maker. The rod was withdrawn, the interior reamed and the exterior filed until the finished tube was achieved. Damascus barrels may be recognized by any of a variety of twist or spiral patterns visible in the surface of the steel. Before the 20th century, barrels were typically built in this manner because gunmakers did not have the technology to drill a deep hole the full length of a bar of steel without coming out the side.

DAO

Abbreviation for Double Action Only. Is a type of firearm in which the firing mechanism cannot be cocked in a single-action stage. Firing always occurs as a double-action sequence where pulling the trigger both cocks and then fires the gun.

Decocker (De-Cocker)

On semi-auto matic pistols, a lever that mechanically lowers the hammer without firing the gun.

Delayed Blowback

A self-loading firearm whose breechblock and barrel are not positively locked together, but which incorporates a mechanism which initially restricts the breechblock from moving when fired, delaying its opening.

Deringer

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

Derringer

A small single-shot or multi-barreled pocket pistol. 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.

Deterrent

A material added to an explosive to slow its burning rate.
Something that will prevent or hinder something from happening.

Detonate

To explode with great violence. It is generally associated with high explosives e.g. TNT, dynamite, etc., and not with the relatively slow-burning smokeless gunpowders that are classed as propellants.

Die

A piece of tooling used to form a sequence of uniform parts through the use of heat and/or pressure; especially, in firearms terminology used to form brass cartridge cases accurately to their correct size for reloading.

Direct Impingement

A type of gas operation for a firearm that directs gas from a fired cartridge directly to the bolt carrier or slide assembly to cycle the action.

Disc-Set Strikers

Circular steel fittings, about 1/2 inch in diameter, screwed into the breech face of a gun and through which the firing pins pass. Firing pin bushings allow the convenient replacement of broken firing pins. They also allow the renewal of an older gun where, over the decades, leakage of high-pressure gas from corrosive primers has eroded the breech face around the firing pins; and replacing these bushings with new ones, slightly oversized can compensate for a situation where proper headspace has been compromised.

Doglock

The lock that preceded the 'true' flintlock in both rifles and pistols in the 17th century. Commonly used throughout Europe in the 1600s, it gained popular favor in the British and Dutch military. A doglock carbine was the principal weapon of the harquebusier, the most numerous type of cavalry in the armies of Thirty Years War and the English Civil War era.

Doll's Head

A rib extension on a break-open gun, ending in a circular or semi-circular shape in plan (resembling the head of a doll), mating into a similarly-shaped recess in the top of the receiver, designed to resist the tendency of the barrels to pull away from the standing breech when firing. Because an action's centerpoint of flexing when firing is at the base of the standing breech, not at the hingepin, a passive doll's head extension makes an effective extra fastener, even without additional mechanical locks operated by the opening lever.

Double Action

An action type that when the trigger of a gun is pulled, the gun gets cocked and the hammer (or striker) is dropped. This applies to both revolvers and semi-automatic guns. On a double action revolver, when the trigger is pulled, the hammer is cocked before releasing. With a double-action semi-automatic pistol, the hammer does not have to be manually cocked (via actually pulling back the trigger or tracking the slide), the hammer (or striker) will be cocked while the trigger is being pulled. A firearm that only the hammer drops when the trigger is pulled is a single action gun.

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.

Double Rifle

Two independent rifles, built on one frame, designed to allow two virtually instantaneously quick, totally reliable shots. The barrels may be arranged either side-by-side or over-and-under. The apogee of the gunmaker's art. Particularly useful against dangerous game, which may be moving, and in your direction, with vengeance on its mind.

Double Tap

Two shots fired in rapid succession. Generally without getting a new sight picture on the target. If the second shot is fired after a second sight picture is captured it may instead be called a controlled pair.

Double Triggers

On guns (mainly shotguns) that have two barrels, there is a trigger for each barrel that work independently from each other.

Double-Barreled Shotgun

A shotgun with two barrels, usually of the same gauge or bore. The two types of double-barreled shotguns are over/under (abbreviated as O/U or OU), in which the two barrels are stacked on top of each other, and side-by-side (abbreviated as SxS), in which the two barrels sit beside each other. See photo at right for example of side-by-side double-barreled shotgun. For double-barreled guns that use one shotgun barrel and one rifle barrel, see combination gun.

Double-Base Powder

A rapidly burning powder made by absorbing nitroglycerine into nitrocellulose (guncotton).

Double-Set Trigger

Usually only found on black powder muzzle loading rifles and pistols, pulling the rear (set) trigger converts the front (main) trigger to a light, hair trigger (too light and sensitive to be carried safely in the field). While the front trigger is always at the ready, if one has the time, using the set trigger feature may allow for a more accurate long-distance shot. Operates using its own miniature firing mechanism (sear, spring and hammer) when cocked, to multiply the force of a pull on the main trigger.

Doughnut Pattern

A shotgun pattern with a hole in the middle generally caused by the interference of the top wad.

Down Range

The area of a gun range where firearms are pointed when they are fired. The area of the range forward of the firing line.

Dram

A unit of measure traditionally used for black powder shotgun charges. Today, used for smokeless powders on the basis of the new propellant's equivalent performance to that weight of black powder. Thus, a shotgun shell marked 3 - 1 1/8 would be loaded with the smokeless powder equivalent of 3 drams of black powder, and with 1 ounce of shot. 1 Dram = 1/16 ounce = 437.5 grains.

Drift

The departure of a bullet or shot charge from the normal line of flight. This can be caused by wind or the unbalanced spinning of the bullet.

Drilling

A three-barrel gun. Typically it has two shotgun barrels side by side on the top, with a third rifle barrel underneath. This provides a very versatile firearm capable of taking winged animals as well as big game. It also is useful in jurisdictions where a person is only allowed to own a single firearm.

Drop Safety

A mechanical safety that prevents a gun from firing when it is unintentionally dropped.

Drop-Box Magazine

An extra-deep magazine typical of large calibre rifles for dangerous game. The line of the underside of the wrist does not carry straight forward as with ordinary rifles. Rather the rear of the magazine aligns more towards the center of the forward edge of the triggerguard, typically allowing at least one extra cartridge to be carried.

Drum Magazine

A type of firearms magazine that is cylindrical in shape, similar to a drum. Probably the most recognizable drum magazine is the magazine for a Thompson carbine rifle, also known as the Tommy Gun.

Dry Fire

To pull the trigger and release the hammer of a firearm without having a cartridge in the chamber.

DST

Abbreviation for Double-Set Trigger

DT

Abbreviation for Double Triggers

Dud

A round of ammunition that does not fire.

Duelling Pistols

Single shot pistols, of a design originating in England, in vogue circa 1770 - 1850, built necessarily in pairs, either of flintlock or percussion ignition, usually finely made and cased together with loading accessories. Dueling pistols tended to be lighter and sleeker than their contemporary service pistols. They tended to have smoothbore (or sometimes secret, scratch-rifling), octagon (or octagon-to-round) barrels around nine or ten inches long of some form of damascus steel, bores just over a half-inch, ramrods, rudimentary sights front and rear, single-set triggers, roller-bearing frizzens and curved grips integral with full or half-stocks. They were usually of high quality construction, sometimes with silver furniture, but normally of relatively plain decoration.

Dum-Dum

A bullet designed to expand on impact, increasing in diameter to limit penetration and/or produce a larger diameter wound. The two typical designs are the hollow point bullet and the soft point bullet. Expanding bullets were given the name Dum-dum, or dumdum, after an early British example produced in the Dum Dum Arsenal, near Calcutta, India by Captain Neville Bertie-Clay in the the mid-1870s. Modern sef-defensive, JHP (Jacketed Hollow Point), ammunition are based on the original dum-dum ammunition design and principles.

Dummy Round

An inert ammunition-shaped object, used in practice to simulate misfeeds and other malfunctions and also used in dry fire practice. Unlike a blank, a dummy round contains no charge at all. A snap-cap is a type of dummy round.

Dust Cover

A small hinged or sliding door covering the ejection port of a firearm to prevent detritus from clogging the works.