Although rifles with twin barrels were made as early as the seventeenth century, the double rifle, as it is understood today, first appeared early in the 19th century, due to sportsmen's need for a rifle capable of firing more than one shot, and doing so in very quick succession. This was during the period of the muzzleloader, when reloading each barrel was a slow, tedious process. The breech-loader form of firearm didn't evolve until the 1860s, and was gradually perfected over time.
Double rifles intended for use on dangerous game came to prominence primarily in India and Africa during the height of the British Empire, and the principal quarry was elephant, tiger, rhino, Cape buffalo, lion and leopard. The double rifle excels over other repeating firearms in its ability to allow the shooter to make a split-second, secondary, follow-up shot on large, dangerous game without having to "work" the firearm's action. This can mean a matter of life or death for the shooter when a large, dangerous animal chooses to charge the hunter, especially in close quarters, and often in thick cover. That is why the double rifle has been a favorite "weapon-of-choice" of many professional hunters of large, dangerous game animals, especially in Africa, both now, and in the distant past.
The earliest breech-loading doubles firing black powder cartridges handled very large cartridges, producing large amounts of smoke on discharge. Some were very large indeed, up to and including, the 4-bore (1.052 inches) calibre. These rifles were so powerful that their recoil could sometimes injure the shooter if fired too many times in succession, although the need to engage in such rapid fire seldom arose. To help counter the effect of the heavy recoil, and to also increase the inherent strength of the individual rifle when chambered for such powerful cartridges, these firearms were necessarily quite heavy, often weighing 15 pounds or more. Though generating tremendous power, the penetrative ability on heavy bone and muscle tissue of these earliest black-powder cartridges was relatively low; this, due to the large (and heavy) size of the projectile itself, coupled with its relatively low velocity. One of the most distinguished and prolific makers of these rifles was W. W. Greener in England.
At the turn of the 20th century black powder was replaced by cordite, and then by smokeless powders based on nitro-cellulose. These propellants enabled smaller-bore, higher-velocity cartridges to be produced, and rifles to be designed for them and their much higher chamber pressures. The smokeless powder cartridges were favored over the cordite, and earlier black-powder loadings, because the smokeless powder cartridges produced less corrosion and fouling inside the rifle bores, and with little to no smoke produced upon firing, it was much easier for the shooter to maintain visual contact with his quarry.
Most double rifles, particularly older ones, are chambered for "rimmed" cartridges. These are cartridges that have a prominent rim at the base of the cartridge case that is of larger diameter than the body of the cartridge case itself. The use of a prominent rim on these cartridges made for easier extraction (via built-in "extractors" within the rifle) whether the rifle had been fired or not. In later development of the double rifle, built-in "ejectors" were included as well. With these, when the firearm was opened, extractors would partially extract the cartridges from the two chambers, and ejectors would "kick" the cartridges free, completely out of the firearm. The latest technological development of the double rifle has seen improvement in the extraction/ejection mechanisms, allowing for the use of "rimless" cartridges whereby the rim at the bottom of the cartridge case is either the same diameter as the body of the cartridge case, or, in some instances, perhaps even "rebated." Further, some newer double rifles even have what might be termed as "smart ejectors." With these, the shooter can fire one barrel, open the firearm to reload the spent cartridge (which will then be ejected free of its respective chamber), yet the unfired round in the other chamber will only be partially extracted throughout the reloading procedure.
The double-barreled express rifle is a particularly difficult firearm to make and "regulate." Regulation of the two barrels is the trial-and-error, time-consuming, painstaking adjustment of the two barrels (and powder charges) prior to permanently fitting the "rib" between the barrels. During regulation of the barrels, the two barrels are mated to the rifle's frame and butt-stock, but the permanent "rib" that goes between the two barrels is not yet installed. Instead, the rifle builder will braze a "temporary" metal wedge between the two muzzles, fire each barrel at a target at a specified distance, then note the point of impact of each projectile on the target, comparing where the projectile fired from the first barrel strikes in relationship to the projectile fired from the second barrel. If the points of impact for the two projectiles on the target are outside the rifle builder's specific parameters, further regulation is called for, with adjustments made to the powder charge and/or the rifle barrels themselves. If the barrels themselves require adjustment, the solder holding the metal wedge in place is heated--freeing up the metal wedge--then the metal wedge is carefully moved incrementally forward, backward, or replaced entirely with a different-sized metal wedge. Each time moving or replacing the metal wedge is called for, the rifle builder must heat the solder, move or replace the metal wedge, then re-braze and test-shoot all over again.
The additional trial-and-error shooting and barrel/powder-charge adjustments go on until the projectiles of both barrels finally strike the target within the builder's specified parameters. Once the builder deems the double rifle is properly "regulated," the metal "rib" is added between the barrels, permanently mating the barrels together. The builder will then specify the exact projectile weight and powder charge used to keep the barrels "in regulation," and this information will be stamped into the metal flats on the top of the frame, underneath the barrels. If, at some later point in time, the shooter of a double rifle chooses to use a bullet weight and/or powder charge that is different than what the firearm was originally regulated for, the firearm will most likely require re-regulation. It should be noted that during the barrel-regulation process, some double rifles will easily "fall into regulation," while others will require considerable time and effort to obtain proper regulation--which, of course, adds to the labor cost and overall expense of the firearm.
By their very design, the two barrels of the double rifle must be aligned very precisely (but this does not mean in parallel) in order for the projectiles to strike at the same point of impact, or nearly so, at a given distance - usually not more than 300 metres, and often much less. The alignment of the barrels is done so that the two projectiles will actually converge at a specified distance, whatever is deemed best for the given caliber and expected range of the quarry. Regarding sights, many modern double rifles will accept mounts to fit a telescopic sight, but most double rifles, particularly those used for dangerous game, are fitted with open sights.
Most of the world's high-quality riflemakers have produced double rifles for their customers, and the most highly-regarded makers include Holland and Holland, James Purdey, John Rigby & Company,Westley Richards, George Gibbs, W. J. Jeffery, and Woodward. Outside the "best gun" London trade, very serviceable double rifles have been made by riflemakers in Germany, Austria, Belgium, France, Italy, and the USA, including makers such as Krieghoff, Merkel and Beretta; however, the "classic" double rifle remains a distinctively English style of sporting firearm.
Many large-calibre double rifles are still in everyday use in Africa, but worldwide, these firearms are now primarily collectors' items or, in the case of older specimens, antiques. Second-hand and auction prices for especially fine and rare double rifles can reach phenomenal figures, up to US$400,000; and few dependable modern double rifles are available for less than US$20,000. In the United States, one builder of modern, well-made double rifles in a variety of calibers is B. Searcy & Company of Boron, California. The price of a new Searcy double rifle starts at US$10,500.00, and goes up considerably, depending on specific model chosen, caliber, and adornment. Since double rifles are hand-fitted, custom-built firearms that require the initial, time-consuming regulation of both barrels, these firearms command very high prices.