Double Gun Terminology

By Chuck Hawks


No one person or firm invented the modern double barreled gun. Although simple in concept, the side-by-side (SxS) shotgun is a mechanically complex mechanism, difficult to produce. (This is why budget priced double guns are seldom satisfactory.) It evolved slowly over a long period of time. British gunmakers contributed the most to the evolution of the breech loading double gun and the nomenclature of double gun parts and assemblies is almost entirely British in origin. Some of the terms employed are confusing to American shooters; hopefully, this article will help to diminish that confusion.

British gunmakers invented most of the actions and features used in practically all double guns today. Enormous creativity and interchange during the last four decades of the 19th Century resulted in the development and perfection of the Purdy and H&H bar action sidelocks, Anson & Deeley boxlock, trigger plate action and Dickson (Scottish) round action. Features such as removable sidelocks, the top lever, Scott spindle, Southgate ejectors, Greener cross-bolt, doll's head, under-bolt, side clips, selective ejectors, selective single triggers, assisted opening, intercepting safety sears, Deeley fore-end latch and Anson fore-end latch were developed and perfected by British gunmakers and adopted by makers of fine double guns around the world. It was during this period that the double gun was brought to full flower.

Double Gun Advantages

A fine double is the queen of shotguns and has many advantages over repeaters. A double barreled shotgun with double triggers is essentially two break-open barreled actions melded together with a common body and stock. If one side malfunctions or a part breaks, the other half of the gun is unaffected and still works correctly. This makes such guns popular for use in the most critical applications.

Double guns offer the shooter an immediate choice of two chokes, a choice he or she can make on the fly, without taking the gun out of service. There is no need to change choke tubes or adjust anything to select the most appropriate choke. A double gun also offers the fastest second shot of all types of firearms, noticeably faster than an autoloader, for example.

Because a break-open gun does away with the long receiver of a pump or autoloader, doubles are generally about four inches shorter than a repeater with the same length barrel. Being shorter and more compact, a properly made double handles and points faster than any repeater. They also generally balance better, typically on the hinge pin. The double's superiority in handling, compared to a repeater, is immediately apparent to an even moderately experienced shooter. A SxS is also, aesthetically, the most graceful and elegant of firearms.

Doubles also run clean. Because the barrels are not opened until well after the shells have been fired, the fouling is contained inside the barrels. The action remains clean inside, even after hundreds or thousands of shots. Normal maintenance requires no disassembly of the mechanism. Just run a Bore-Snake or cleaning rod through the barrels and wipe off the exterior with a silicone cloth after shooting.

Double Gun Basics

The barrels of a double gun are hooked over a large hinge pin at the front of the action bar. The fore-end snaps into place to a lug called a "loop" beneath the barrels. Once in place, the fore-end iron keeps the barrel hook at the front of the lump over the action body's hinge pin when the gun is opened, so the barrels cannot fall off.

Top levers, mounted on the top tang, rotate a Scott spindle to unbolt the barrels and allow them to pivot downward for loading and unloading. Break-open guns are loaded manually. The shooter simply inserts a shell into each chamber and closes the gun. As the barrels of a "hammerless" gun pivot down, cocking rods contact the concealed hammers inside the locks and force them back to the full cock position, ready for firing after the gun is loaded and the barrels are manually closed.

In addition, opening the action and pivoting the barrels down activates extractors that raise fired (or unfired) shells so they can be manually extracted, or ejected if the extractors are combined with ejectors. Guns equipped with automatic ejectors will extract unfired shells for manual removal and eject fired shells when the barrels are opened. Almost all best grade field guns are equipped with automatic ejectors, but guns intended for shooting clay targets or live pigeons may not be, at the customer's option.

Some guns are equipped with an assisted opening mechanism designed by Frederick Beesley and popularized by the famous firm of James Purdy & Sons. (Beesley also patented methods for cocking both sidelock and boxlock "hammerless" [internal hammer] double guns and was the principle designer of the famous Purdy sidelock action.) The Beesley self-opening system kicks the barrels open when the top lever is operated, withdrawing the bolts.

Naturally, the springs that power the assisted opening mechanism must be compressed when the gun is closed, which makes the gun easy to open, but harder to close. Many top of the line British and Spanish shotguns incorporate assisted opening, although most North American shooters prefer guns without this feature. I don't know of any double gun made in the USA that came standard with assisted opening.

Methods of Joining Barrels

The barrels of a double barreled gun must be joined together. Here are the ways this is normally accomplished.

1. Chopper lump: Chopper lump barrels have half a lump forged integrally with a full length barrel tube. (The result vaguely resembles what the British call a "chopper," or axe.) These half lumps are then brazed together, forming a complete lump and holding the barrels together. This method of construction creates the narrowest (across the breech) and lightest possible set of barrels and chopper lump barrels are generally considered to be the very best. However, it is also the most difficult and time consuming method of joining side-by-side barrels, requiring much skilled hand labor to get right. Chopper lump barrels can be identified by a very fine longitudinal line where the lumps are joined, usually visible in the polished bottom of the lumps.

Chopper lump barrels are found in virtually all London best and Spanish best guns. The best Italian doubles also use chopper lump barrels. Miroku of Japan used chopper lump barrels in SxS guns manufactured for Charles Daly and Browning. Some Belgian, French and German best doubles are also made with chopper lump barrels.

2. Demi-block: A variation on the chopper lump is the dovetail lump. Henri Pieper, a Belgian gunmaker credited with inventing this system, coined the term "demi-block" for his dovetailed chopper lump tubes. Demi-bloc barrels are similar to chopper-lump barrels, with a half of the lump integral with each barrel tube. They differ from traditional chopper-lump barrels in that the two half lumps incorporate a male and female vertical dovetail. The male and female dovetail lumps slide together and are then pinned and soldered in place. (Rather than brazed, which requires higher temperatures and is harder on the steel.) This produces joined barrels that are stronger than chopper lump tubes, although slightly wider across the breech. This is the method used in the Winchester Model 21 and, I believe, current Merkel doubles.

A word of caution is necessary here. The term "demi-block" has been used (or perhaps misused) by some European manufacturers to describe chopper lump barrels and by others to describe through-lump barrels. (In the latter case, the through-lump is presumably the demi-block.) Hence, some guns advertised with demi-block barrels may not actually have dovetailed chopper lump barrels.

3. Through-lump: Less expensive and easier to manufacture than chopper lump barrels or dovetailed chopper lump barrels is the through-lump. The through-lump is a separate piece of steel machined with the lump(s) on the bottom to which the two individual, full length, barrels are fitted and brazed. This is a satisfactory and simpler method of construction, although not as elegant as chopper lump or demi-block tubes, and usually results in barrels that are somewhat wider across the breech. It is used in the less expensive British double guns, some German guns and all of the classic American doubles, except the Winchester Model 21.

Another word of caution: Through-lump barrels are sometimes called "dovetailed barrels," creating confusion with demi-block barrels that use dovetailed chopper lump tubes. It is a confusing world.

4. Monoblock: Whether chopper lump, demi-block or through-lump, the barrels are stuck full length. Monoblock barrels are not. In the monoblock system, developed (I believe) by Beretta, barrel tubes without chambers are fitted into a steel block machined to form both the chambers and lumps. Such barrels normally have a fine, visible line about 3-4 inches in front of the breech, which is often concealed by a ring of border engraving. Monoblock barrels are widely used in medium priced Italian doubles and some others, including the American made Ruger Red Label O/U and Gold Label SxS.

5. Comments: Other things being equal, the demi-block (dovetailed lump) is the strongest method of joining barrels. The chopper-lump method is considered stronger than barrels joined with a through-lump. However, all of these traditional methods of barrel joining work satisfactorily if done properly. The simpler and less labor intensive monoblock system also works well and some nice guns are made this way.

Barrel Ribs

After the barrels are assembled together, top and bottom ribs are used to close the space between the barrels. The bottom rib is a long, thin strip of steel that is gently concave to match the curve of the underside of the barrels.

The top rib can be concave (as in most traditional British style field guns), a solid raised rib with a concave or flat top surface (found on most American and German guns), or a ventilated raised rib (most commonly used on competition guns, such as the Winchester Model 21 Trap Grade).

Fore-end

The fore-end is the wood directly in front of the receiver. The fore-end keeps the barrels on the hinge pin when the gun is opened and it usually contains the ejector mechanism. The common types of fore-end designs include splinter, semi-beavertail and beavertail.

The splinter fore-end is typical of British, Spanish and many other SxS guns. It is a graceful design: short, narrow and slender. It is big enough to do its job of keeping the barrels attached to the action and to house the ejector mechanism, but not big enough to keep the shooter's fingers off the barrels when shooting. However, it is generally the sleekest and most attractive form of fore-end and is widely used on upland game guns.

The beavertail fore-end is most often found on competition trap and skeet guns. It is long, wide and extends well up the side of the barrels. It is designed to keep the shooters fingers off of the barrels, which can become quite hot during competition events where 100 targets are shot consecutively. Much larger than a splinter fore-end, the beavertail is probably more functional, but not as attractive and, of course, heavier.

The semi-beavertail is an attempt to strike a reasonable balance between the small splinter fore-end and the big beavertail. Thus, it is between the splinter and beavertail in length, width, overall size and weight. It is just big enough to (mostly) keep the shooter's fingers off of the barrels for field shooting purposes.

There are, of course, many different variations of these three basic fore-end styles. For those who are interested, the Winchester Model 21 catalog shows typical American interpretations of each type.

The fore-end is kept in place by a spring or some form of mechanical latch that attaches to the loop soldered or brazed beneath the barrels. The cheapest guns often use a simple, over-center spring mechanism to retain the fore-end. More sophisticated guns use a mechanical fore-end latch.

The best and most common of these are the spring loaded Anson pushbutton latch, located at the tip of the fore-end, and the Deeley latch, a lever inletted into the middle of the fore-end. Other forms of mechanical fore-end latch are sometimes seen, such as the roller latch used in the Winchester Model 21.

Buttstock

The buttstock allows the gun to be fired from the shoulder. It is attached to the rear of the gun's action body. Sometimes this is accomplished by a draw-bolt that runs through the length of the stock and is hidden behind the butt plate. More commonly on double guns, screws through the top and bottom tangs are used to hold the buttstock in place.

The "hand" is the part of the stock gripped by the shooting hand and it should correctly position the trigger finger to fire the gun. A straight hand grip is typically (but not exclusively) found on double trigger guns, as it facilitates the slight fore and aft hand movement required to optimally position the trigger finger between shots for the front and back triggers. Many experienced double gunners prefer the look and feel of a straight hand stock, even on single trigger guns.

Pistol grip hands are also popular on double guns. The Prince of Wales grip is probably the most elegant of these. It has a very gentle curve that is usually terminated in a rounded knob sans cap. The Browning Superposed Lightning model over-under gun popularized this type of hand in the US. This style works well with both double and single trigger guns.

More curved pistol grips should be segments of a circle. They position the hand in a more fixed position and are best used with single trigger guns.

Shotgun hands should never have hooked or abrupt curves, as seen on some rifles. These cramp the shooting hand and slow mounting the shotgun. Pistol grips often, but not always, are terminated with a cap made of ebony, rosewood, horn, steel or plastic.

The top of the buttstock is called the comb. The comb positions the shooter's eye to look down the barrels. A shotgun has no rear sight and is not aimed like a rifle. The comb should properly position the shooter's eye and, in effect, serves as the gun's rear sight.

The comb should position the shooter's eye slightly above the barrels. The shotgunner looks slightly down on the barrels, seeing them greatly foreshortened at the bottom of his or her field of view. This lets the shooter focus and concentrate on the target and slightly compensates for rising birds.

The comb should be straight and close to level when the gun is shouldered to minimize the effect of recoil. A stock with a lot of drop at comb tends to shoot low and is liable to rap the shooter's face when the gun is fired.

Sophisticated stocks are often slightly bent or curved away from the shooter's face. This is called "cast off" and facilitates quick gun mounting and eye alignment over the barrels. However, too much cast off can jam the comb into the shooter's cheekbone when the gun recoils.

"Pitch" refers to the angle of the buttplate. Too little pitch down makes the gun shoot high and tend to slip off the shoulder. Too much pitch down makes the gun shoot low.

Another subtle stock feature found on best gun stocks is "twist." The stock is carved with a slight twist, so the butt matches the angle of the shooter's shoulder pouch when the gun is shouldered.

When a shooter is measured for a bespoke double gun, these factors are taken into consideration and become part of the stock design. Cumulatively, they make the gun faster, easier and more comfortable to shoot. The difference, compared to the "one size fits all" stocks found on mass produced repeaters, is very apparent.

SOME DOUBLE GUN TERMS & DEFINITIONS

Action bar: The part of a double gun action extending forward of the standing breech and below the barrels.

Action body: The metal housing, or receiver, for the guns's action.

Bar: See "Action bar."

Barrel flats: The flat undersurface of the barrels (below the chamber area) that mates to the flats on the action bar.

Bite: The slot cut into the rear of the lumps that is engaged by an under bolt to hold the barrels closed. Actions that use only top bolts do not have bites in the lumps.

Bolt: The device(s) that hold the barrels closed are called "bolts," as in under bolts or top bolts. The bolt is operated by a shaft (Scott spindle) connected to the top lever. Under bolts, devised by James Purdy and located in the big slot in the action bar, engage the bites of the lumps to hold the barrels closed. British and Spanish best guns typically use double sliding under bolts. The Winchester Model 21 uses a single under bolt.

Top bolts engage a heavy extension of the top rib to hold the barrels closed. The Greener cross-bolt and rotary bolts are examples of commonly used top bolts.

Boxlock: Double gun mechanism invented in Britain by Anson and Deeley, employees of the Westley Richards firm, and still in wide use today. Boxlock actions contain the lock parts within the rear portion of the action body.

Doll's head: Designed by Westley Richards, the doll's head is a compact top rib extension that fits into the top tang. It uses no bolt and does not serve to prevent the barrels from rotating open about the hinge pin. However, it does strengthen the action by resisting the force upon firing that attempts to break the action bar where it meets the standing breech. This is the point of greatest stress when a break-open action gun is fired and the Doll's head is an effective reinforcement. The famous American Parker action used a doll's head, as have some guns from such famous British makers as Westley Richards and Charles Boswell.

Dovetail: Another term applied to a through-lump.

Face: The standing breech; the vertical part of the action against which the barrels are held closed.

Flats: The upper surface of the action bar that fits against the flat underside of the barrels.

Hinge pin: The large diameter pin at the front of the action bar on which the barrels revolve up and down.

Hook: The semi-circular recess at the front of the lump that hooks over the hinge pin at the front of the gun's action bar.

Interceptor: Also called "interceptor sear" and "safety sear." See definition below under "safety sear."

Knuckle: The front of the action bar against which the barrels, held in place by the hinge pin, rotate.

Locks: The firing mechanisms of double guns are called "locks," as in sidelock or boxlock. The locks fire the gun, they do not hold it closed.

Loop: The lug soldered beneath the barrels, several inches in front of the action bar, to which the fore-end iron attaches to hold the fore-end in place.

Lumps: The large projections on the bottom of the barrels at the breech end. Slots cut into the lumps, called "bites," are engaged by the (under) "bolts" that hold the barrels closed.

Purdey under bolt: A sliding, tapered rectangular bolt that runs longitudinally through the action bar. This bar retracts when the top lever is pressed to the side to allow the barrels to open and it moves forward under spring tension when the top lever is released, allowing its locking surfaces to engage the bites in the rear of the lumps when the barrels are closed. In modern doubles the under bolts are retracted by a cam at the bottom of the top lever spindle. This bolting system, common in best guns since the last quarter of the 19th Century, was originally designed by James Purdey.

Safety sear: A lock part designed to catch the hammer should it slip or be jarred from its full cock position, thus preventing an accidental discharge. Pulling the trigger moves the safety sear out of the way. Both Holland & Holland and Purdy type sidelocks incorporate safety sears.

Scott spindle: When the top lever is pressed to open a double gun, it rotates a shaft (or spindle) with a cam at the bottom that mechanically retracts the under bolts that holds the barrels closed. This system was devised by William Scott.

Sidelock: Sidelock actions use side plates, located behind the action body, to which the lock parts are attached. These side plates are inletted into the stock.

In a bar action sidelock, part of the mechanism (typically the big hammer spring) attached to the side plate extends forward into the frame's action bar. Less common today is the back action sidelock, where all lock parts are behind the action body. Purdy and Holland & Holland bar action sidelocks are the most common (and most copied) types of sidelock.

Single trigger: In addition to the obvious solution of using a separate trigger to fire each barrel of a double gun (double triggers), a single trigger can be used to fire the barrels of a double gun one after the other with two pulls on the same trigger. The simplest type of single trigger is designed to fire one barrel and then, with a second pull of the trigger, the other barrel. This type of single trigger is reliable, but always fires the barrels in the same order, usually the barrel with the more open choke first.

A selective single trigger (SST) can fire either barrel first and then resets to fire the second barrel. The barrel to be fired first is usually selected by lateral movement of the top tang safety, or by a cross-bolt type button in the top of the trigger blade.

Single selective trigger mechanisms are surprisingly complicated and many SST designs are subject to doubling (firing both barrels with a single pull of the trigger) or balking (failing to reset to fire the second barrel). Probably the best and most reliable of the breed are the mechanical selective single trigger used in the Winchester Model 21 SxS gun and the recoil operated (inertia) SST used in the Browning Superposed and Citori O/U guns. Both of these triggers work very well.

Most British and Spanish best gun makers mistrust selective single triggers and their guns generally have double triggers, or at most a non-selective single trigger. On the other hand, many American shooters prefer single triggers and modern American and Continental guns intended for the American market frequently have selective single triggers.

Southgate ejectors / Hammer ejectors: A type of ejector that uses small, spring powered hammers located in the fore-end to forcefully drive the extractors back to eject fired shells. Southgate ejectors are more powerful and reliable than ejectors that rely on direct spring actuation.

Standing breech: The "face" of the action body; the vertical part of the action against which the barrels are held closed.

Strap: Another word for tang. See below.

Tang: Rearward extensions behind the action body. There are top and bottom tangs on a double gun to which the buttstock is normally attached. The top tang is also where the top lever is located.

Top bolt: A bolting device that engages a top extension to keep the barrels closed. Being the farthest point from the hinge pin, a top bolt engaging a top extension has the greatest leverage to keep the barrels closed, which makes it very attractive from the engineering standpoint. Most American and Continental doubles use a top bolt fastener, as do a few British guns.

Top extension: Jutting back over the breech of many double guns and fitting into a slot in the top tang is an extension behind the top rib. This top extension typically has a hole for a Greener cross-bolt or deep notches that accept a rotary or sliding bolt used to hold the barrels closed.

Top lever: Located on the action's top tang, this is the lever used to unlock the barrels so they can drop open.

Tumbler: The British term for hammer assembly. The tumbler includes the integral hammer (on internal hammer actions), the front arm, notches, axles and body. The tumbler is usually a single part, unless the gun has external hammers. In that case the external hammers are a separate part connected to an internal tumbler that engages the sear, etc.

Under bolt: See "bolt."

THE END




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Copyright 2016 by Chuck Hawks. All rights reserved.


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