Browning Auto-5 shotgun of early Belgian manufacture, left side
Browning Auto-5 shotgun of early Belgian manufacture, right side
Advertising from pre-WW1 era Russian mail-order hunting supplies catalog that offered "New autoloading shotgun, five-shot, Browning system, made by Fabrique Nationale"
Browning Auto-5 "12 gauge Light model" shotgun of late Belgian manufacture
Browning Auto-5 shotgun of Belgian manufacture in military configuration, as used by British forces under L32A1 designation
Browning Auto-5 shotgun of Belgian manufacture, special version for police use, with factory extended 8-round magazine
Early production Remington model 11 shotgun, commercial model
Remington model 11 shotgun in "Riot" configuration, for police or guard use
Remington model 11 shotgun with recoil pad and Cutts compensator, as used by USAF during WW2 to train aircraft machine gunners.
Remington model 11 shotgun set up into special mount to emulate aircraft machine gun. This setup was used by US Air Force during WW2 to train aircraft machine gunners on shooting at moving targets
Type: semi-automatic, recoil operated
Gauge: 12, 16 and 20
Length: varies with model
Barrel length: varies with model
Weight varies with model
Capacity: 4 rounds in underbarrel tube magazine
John Moses Browning, the legendary American gun designer, invented the first practical self-loading shotgun in 1898. In fact, Browning designed and patented three different systems, but finally choose the last one to go ahead. It must be noted, that at the time the autoloading shotgun was something of absolute novelty, and the task of designing such gun was severely complicated by the fact that the switch over from black powder to smokeless ammunition was well under way, and general quality of shotgun ammunition was rather uneven, to say the least. Nevertheless, Browning managed to make hist prototype model work, and work well. He first offered this shotgun to Winchester, which was the sole buyer for his designs from 1886 on. However, severe technical conservatism on the part of the Winchester's boss, T.G.Bennett, and financial disagreements (Browning insisted on royalty-based payments, but Winchester at the time always bought new designs for fixed amount of money) resulted in break between the designer and the company. Browning then turned to Remington, but tragic death of the Remington's president from hear attack just minutes before scheduled meeting with Browning put an end to this route as well. Browning then turned to the Belgian company Fabrique Nationale (FN), which at this time (1901) produced first Browning-designed selfloading pistol (M1900) as fast as it could be made. FN management greeted Browning and his new gun with great enthusiasm, and in a short while FN produced the first FN Browning autoloading shotgun, known as Browning Auto 5, or A-5 in short. Browning himself ordered 10,000 A-5 shotguns from the first batch for sales and distribution in USA, and sold all 10 thousands in about a year. Following the introduction of the new, increased custom tariffs by US government, Browning found that it was economically not reasonable to import more A-5 guns into USA, so he pursued FN to release rights to make and sell Browning autoloading shotgun on US market to Remington Arms Co (FN originally had worldwide rights for manufacture of Auto 5). In 1906 Remington offered the Browning-designed autoloading shotgun as Model 11, and manufactured it without interruption until 1947, with well over 800,000 guns made. Between 1949 and 1968 Remington also produced an updated (lightened and streamlined) version of the Browning's design, known as Remington Model 11-48. The FN produced Browning Auto 5 shotguns continuously (with interruptions for German occupation during both World Wars) until 1999, making Auto-5 probably the most successful and longest-producing sporting shotgun in the history. Overall output of Auto-5 shotguns made and sold by FN (During WW2, A-5 shotguns were made for Browning Arms Co by Remington, and since mid-1970s Auto-5 shotguns were also produced for FN in Japan by Miroku, under FN license) over the century well exceeds two million guns (2,000,000th Auto-5 was produced in 1970). Total estimate of worldwide production numbers for this legendary Browning design is well over three million guns.
Copies and clones of the Auto-5 shotgun were also manufactured in Italy by Franchi and Breda, in USA by Savage and in USSR / Russia by TOZ, and by some other manufacturers around the world. Many Auto-5 guns, made many decades before, are still used for hunting and shooting today, but, as time goes, Browning Auto-5 shotguns increasingly become collector's pieces.
Over the time, both FN and Remington produced wide variety of versions of the basic design. Hunting guns were made with plain or ribbed barrels of various lengths and gauges (12, 16 and 20), with magazine capacities of 4 or 2 rounds, various stocks, finishes etc. For police and military applications, FN and Remington created shorter-barreled shotguns with plain barrels. Many Remington guns have seen extensive use by US police and security services; US military also used Remington shotguns to train AA and aircraft gunners in shooting at fast-moving flying targets (clay pigeons), using traditionally stocked guns or guns, mounted in special fixtures to emulate aircraft machine guns. Belgian-made guns have seen less military service, although British army issued more than few A-5 shotguns as L32A1 during Malay counter-insurgency operations and later.
Browning Auto-5 shotgun uses recoiling barrel to operate its action. The system is of so-called long-recoil type, as barrel and bolt recoil together for entire length of the recoil stroke, being securely locked by pivoting piece, installed in the bolt. This piece, when pivoted up, engages the cut in the barrel extension with its large locking lug. Upon completion of the full recoil path, the bolt is arrested in the rearmost position, and the locking piece inside it is tipped down to release the barrel. Barrel, under pressure of its own return spring, located around the magazine tube, slams forward, leaving the empty shell on the bolt face. Once the empty shell is clear of the barrel, it is ejected out of the gun. When barrel comes to the rest in the forward position, it automatically releases bolt catch, allowing the bolt to run forward, picking the fresh cartridge from the raised cartridge lifter, and locking the to the barrel at the end of the forward run. Bolt return spring is located in the butt. To achieve reliable functioning with wide variety of loads, Browning used self-adjusting friction brake in the recoil system, which consisted of several (one or two, depending on the exact model) friction rings, located around the magazine tube. The tubular magazine holds four rounds; fifth one can be loaded into the chamber, making the total capacity of five rounds. One important difference between FN Auto-5 and Remington Model 11 shotguns is that the FN guns had a magazine cut-off lever, located on the left side of the receiver. This lever, when turned to the rear, locks the cartridges in the magazine, allowing for quick replacement of the loaded round with another (presumably, with different type of projectile(s), i.e. shot to slug or vice versa). Remington shotguns did not have this feature.
The shotgun is probably the oldest type of all shoulder-fire firearms. Many earliest guns were smoothbore and loaded with multiple projectiles simultaneously. The shotguns were and still are used for hunting, since multiple projectiles increase the chances to hit the target with one shot, but shotguns also were used in combat in almost all wars since their introduction. The devastating short-range firepower and flexibility in loads are the key advantages of shotguns as the fighting weapons. During the XX century shotguns seen lot of combat, both as a police riot weapons and as a military trench, and later - jungle and urban close quarters battle weapons. Police used shotguns for riot and crowd control, and as a general purpose short and medium range weapons for about 150 years. First well known military use of shotguns is dated back to the Great War (1st World War), when Allied forces used various pump-action and self-loading shotguns in the trench warfare. During the 2nd World War shotguns were used as a security weapons (for guarding and anti-riot purposes), for close combat in jungle environments of SE Asia, where the self-loading shotguns (like the Remington 11 and Auto-5 - both of Browning design) proved to be very valuable for their devastating short-range firepower. The shotguns were also used for aerial gunnery training. Vietnam war also seen many shotguns used by US troops in the jungles, but these were mostly pump-action shotguns. At the present time shotguns formed a valuable part of equipment of both police and military forces around the world, and its development continued. There were several programs intended to increase shotguns effectiveness and combat range, but these proved mostly to be less than successful. Most combat shotguns were and still are the adaptations of commercial, hunting firearms for the new role, but during the last three decades of the XX century some specialized combat shotguns were developed. Some of these remained only in prototype or pre-production status, others flourished and found its way into the police and military stocks. 
Semi-automatic shotguns can use several different actions - inertia recoil (Benelli), gas (Russian AK-47-derived Saiga-12 and Italian Franchi SPAS-15), barrel recoil (Browning designed Auto-5 and Remington 11). Semi-autos usually have less recoil (especially gas-operated ones), and higher rate of fire, but somewhat more sensitive to the loads selection. The greater firepower, offered by semi-automatic shotguns, is especially useful for military applications, where short-range encounters are usually very rapid, and the amount of firepower used in a short period of time is essential to win the scenario and save one's life.