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In 1980, the Austrian military announced that it would seek tenders for a new, modern duty pistol to replace their World War II-era Walther P38 handguns. The Austrian Ministry of Defence formulated a list of 17 criteria for the new generation service pistol. 1. The design has to be self-loading. 2. The pistol must fire the NATO-standard 9×19mm Parabellum round. 3. The magazines would not require any means of assistance for loading. 4. The magazines must have a minimum capacity of 8 rounds. 5. All actions necessary to prepare the pistol for firing and any actions required after firing must be done single-handed, either right- or left-handed. 6. The pistol must be absolutely secure against accidental discharge from shock, stroke and drops from a height of 2 meters onto a steel plate. 7. Disassembly of the main parts for maintenance and reassembling must be possible without the use of any tools. 8. Maintenance and cleaning of the pistol must be accomplished without the use of tools. 9. The pistol's construction may not exceed 58 individual parts (equivalent of a P38). 10. Gauges, measuring and precise testing devices must not be necessary for the long-term maintenance of the pistol. 11. The manufacturer is required to provide the Ministry of Defence with a complete set of engineering drawings and exploded views. These must be supplied with all the relevant details for the production of the pistol. 12. All components must be fully interchangeable between pistols. 13. No more than 20 malfunctions are permitted during the first 10,000 rounds fired, not even minor jams that can be cleared without the use of any tools. 14. After firing 15,000 rounds of standard ammunition, the pistol will be inspected for wear. The pistol will then be used to fire an overpressure test cartridge generating 5,000 bar (72,518 psi) (the normal maximum operating pressure Pmax for the 9 mm NATO is rated at 2,520 bar (36,550 psi)).[9] The critical components must continue to function properly and be up to specifications, otherwise the pistol will be disqualified. 15. When handled properly, under no circumstances may the user be endangered by case ejection. 16. The muzzle energy must be at least 441.5 J when firing a 9mm S-round/P-08 Hirtenberger AG. 17. Pistols scoring less than 70% of the total available points will not be considered for military use. The Glock Safe Action Pistol, colloquially known as the Glock is a series of semi-automatic pistols designed and produced by Glock Ges.m.b.H., located in Deutsch-Wagram, Austria. The company's founder, engineer Gaston Glock, had no experience with firearm design or manufacture at the time their first pistol, the Glock 17, was being prototyped. Glock did, however, have extensive experience in advanced synthetic polymers, knowledge of which was instrumental in the company's design of the first successful line of pistols with a polymer frame. Glock introduced ferritic nitrocarburizing into the firearms industry as an anti-corrosion surface treatment for metal gun parts. Glock became aware of the Austrian Army's planned procurement and in 1982 assembled a team of Europe's leading handgun experts from military, police and civilian sport shooting circles to define the most desirable characteristics in a combat pistol. Within three months, Glock developed a working prototype. The new weapon made extensive use of synthetic materials and modern manufacturing technologies in its design, making it a very cost-effective candidate. Several samples of the 9x19mm Glock 17 (so named because it was the 17th patent of the company) were submitted for assessment trials in early 1982, and after passing all of the exhaustive endurance and abuse tests, Glock emerged as the winner with the Model 17. The handgun was adopted into service with the Austrian military and police forces in 1982 as the P80 (Pistole 80),with an initial order for 25,000 guns. The Glock 17 outperformed 8 different pistols from five other established manufacturers (Heckler & Koch offered their P7M8, P7M13 and P9S, SIG-Sauer of Switzerland bid with their P220 and P226 models, Beretta of Italy submitted their model 92SB-F, FN Herstal proposed an updated variant of the Browning Hi-Power and the home-grown Steyr entered the competition with the GB). The results of the Austrian trials sparked a wave of interest in Western Europe and overseas, particularly in the United States, where a similar effort to select a service-wide replacement for the M1911 had been ongoing since the late 1970s (known as the Joint Service Small Arms Program). In late 1983, the United States Department of Defense inquired about the Glock pistol and received four samples of the Glock 17 for unofficial evaluation. Glock was then invited to participate in the XM9 Personal Defense Pistol Trials, but declined because the DOD specifications would require extensive retooling of production equipment and providing 35 test samples in an unrealistic time frame. Shortly thereafter, the Glock 17 was accepted into service with the Norwegian, and Swedish Armed Forces, surpassing all prior NATO durability standards.[16] As a result, the Glock 17 became a standard NATO-classified sidearm and was granted a NATO Stock Number (1005-25-133-6775). By 1992, some 350,000 pistols had been sold in more than 45 countries, including 250,000 in the United States alone. Despite initial resistance from the market to accept a "plastic gun" due to durability and reliability concerns, Glock pistols have become the company's most profitable line of products, commanding 65% of the market share of handguns for United States law enforcement agencies as well as supplying numerous national armed forces and security agencies worldwide. Development A "first generation" Glock 17 with the slide locked back displaying its upward barrel tilt A "second generation" Glock 17, identified by the checkering on the front and rear straps of the pistol grip and trigger guard An early "third generation" Glock 19, identified by the addition of thumb rests, an accessory rail, finger grooves on the front strap of the pistol grip and a single cross pin above the trigger A "third generation" Glock 17C, identified by the addition of an extra cross pin above the trigger and a reshaped extractor that serves as a loaded chamber indicator Product evolution The Glock was modified several times throughout its production history. In 1991, an integrated recoil spring assembly replaced the original two-piece recoil spring and tube design. The magazine was slightly modified, changing the floorplate and fitting the follower spring with a resistance insert at its base. Second generation models A mid-life upgrade to the Glock pistols involved the addition of checkering on the front strap and serrations to the back strap. These versions were introduced in 1988 and are informally referred to as "second generation" models. To meet American ATF regulations, a steel plate with a stamped serial number was embedded into the receiver in front of the trigger guard. Third generation models In the late 1990s, the frame was further modified with an accessory rail (called the "Universal Glock rail") to allow the mounting of laser sights, tactical lights, and other accessories. Thumb rests on both sides of the frame and finger grooves on the front strap were added. Glock pistols with these upgrades are informally referred to as (early) "third generation" models. Later third generation models additionally featured a modified extractor that serves as a loaded chamber indicator, and the locking block was enlarged, along with the addition of an extra cross pin to aid the distribution of forces exerted by the locking block. This cross pin is known as the locking block pin and located above the trigger pin. The polymer frames of third generation models can be black or olive drab. Besides that, non-firing dummy pistols ("R" models) have a bright red frame and Simunition-adapted practice pistols ("T" models)—a bright blue frame for easy identification. In 2009, the Glock 22 RTF2 (Rough Texture Frame 2) (chambered in .40 S&W) was introduced. This pistol featured a new checkering texture around the grip and new scalloped (fish gill shaped) serrations at the rear of the sides of the slide. Fourth generation models Comparison of "third" (left) and "fourth" generation (right) Glock 19 grip frames At the 2010 SHOT Show, Glock presented the "fourth generation" design, with updates centered on ergonomics and the recoil spring assembly. The fourth generation has no total parts modularity with its predecessors, meaning not all parts can be mixed and matched with previous Glock generations. The initial two fourth generation models announced were the full-size Glock 17 and Glock 22, chambered for the 9x19mm Parabellum and .40 S&W cartridges, respectively. The pistols were displayed with a modified rough texture frame, grip checkering, and interchangeable backstraps of different sizes. "Gen4" is rollmarked on the slide next to the model number to identify the fourth generation pistols. The basic grip size of the fourth generation Glock pistols is smaller compared to the previous design. A punch is provided to remove the basic trigger housing pin and replace it for the longer cross pin needed to mount the "M" (medium) or "L" (large) backstrap. With the medium-sized backstrap installed, the grip size is comparable to the third generation pistols. The magazine release catches are enlarged and reversible for left-handed use. To utilize the swappable magazine release feature, fourth generation Glock magazines have two notches cut on both sides of the magazine body. Mechanically, fourth generation Glock pistols are fitted with a dual recoil spring assembly to help reduce perceived recoil and increase service life expectancy (earlier subcompact Glock pistols already used a double recoil spring configuration, which was carried over to the fourth generation versions of those variants). The slide and barrel shelf have been resized due to the larger diameter of this dual recoil spring assembly. The front portion of the polymer frame under the slide has been widened and internally enlarged in order to accommodate the dual recoil spring assembly. The trigger mechanism housing has been dimensionally adapted to fit in the smaller sized grip space. The introduction of fourth generation Glock pistols continued in July 2010 when the Glock 19 and Glock 23, the reduced size "compact" versions of the Glock 17 and Glock 22, became available for retail. In late 2010 Glock continued the introduction of fourth generation models with the Glock 26 and Glock 27 "subcompact" variants. Design details Operating mechanism The Glock 17 is a 9mm short recoil-operated locked breech semi-automatic pistol that uses a modified Browning cam-lock system adapted from the Hi-Power pistol. The firearm's locking mechanism utilizes a linkless, vertically tilting barrel with a rectangular breech that locks into the ejection port cut-out in the slide. During the recoil stroke, the barrel moves rearward initially locked together with the slide approximately 3 mm (0.12 in) until the bullet leaves the barrel and chamber pressure drops to a safe level. A ramped lug extension at the base of the barrel then interacts with a tapered locking block integrated into the frame, forcing the barrel down and unlocking it from the slide. This camming action terminates the barrel's movement while the slide continues back under recoil, extracting and ejecting the spent cartridge casing. The slide's uninterrupted rearward movement and counter-recoil cycle are characteristic of the Browning system. Features A subcompact Glock 30 field stripped to its main parts with a .45 ACP round The slide features a spring-loaded claw extractor and the stamped sheet metal ejector is pinned to the subframe. Post 2002 pistols have a reshaped extractor that serves as a loaded chamber indicator. When a cartridge is present in the chamber, a tactile metal edge protrudes slightly out immediately behind the ejection port on the right side of the slide. The striker firing mechanism has a spring-loaded firing pin that is cocked in two stages, powered by the firing pin spring. When the pistol is charged, the firing pin is in the half-cock position. As the trigger is pulled, the striker is then fully cocked. At the end of its travel, the trigger bar is tilted downward by the disconnector, releasing the striker to fire the cartridge. The disconnector resets the trigger bar so that the striker will be captured in half-cock at the end of the firing cycle. This is known as a pre-set trigger mechanism, referred to as the "Safe Action" trigger by the manufacturer. The disconnector ensures the pistol can only fire semi-automatically. The factory-standard two-stage trigger has a trigger travel of 12.5 mm (0.5 in) and is rated at 25 N (5.6 lbf), but by using a modified connector it can be increased to 35 N (7.9 lbf) or lowered to 20 N (4.5 lbf). In response to a request made by American law enforcement agencies for a two-stage trigger with increased trigger pull, Glock introduced the NY1 (New York) trigger module, which features a flat spring in a plastic housing that replaces the trigger bar's standard coil spring. This trigger modification is available in two versions: NY1 and NY2 that are rated at 25 N (5.6 lbf) to 40 N (9.0 lbf) and 32 N (7.2 lbf) to 50 N (11.2 lbf) respectively, which require approximately 20 N (4.5 lbf) to 30 N (6.7 lbf) of force to disengage the safeties and another 10 N (2.2 lbf) to 20 N (4.5 lbf) in the second stage to fire a shot. The Glock's frame, magazine body and several other components are made from a high-strength nylon-based polymer invented by Gaston Glock and called Polymer 2. This plastic was specially formulated to provide increased durability and is more resilient than carbon steel and most steel alloys. Polymer 2 is resistant to shock, caustic liquids and temperature extremes where traditional steel/alloy frames would warp and become brittle. The injection molded frame contains 4 hardened steel guide rails for the slide: two at the rear of the frame, and the remaining pair above and in front of the trigger guard. The trigger guard itself is squared off at the front and checkered. The grip has a non-slip, stippled surface on the sides and both the front and rear straps. The frame houses the locking block, which is an investment casting that engages a 45° camming surface on the barrel's lower camming lug. It is retained in the frame by a steel axis pin that holds the trigger and slide catch. The trigger housing is held to the frame by means of a plastic pin. A spring-loaded sheet metal pressing serves as the slide catch, which is secured from unintentional manipulation by a raised guard molded into the frame. The Glock pistol has a relatively low slide profile, which holds the barrel axis close to the shooter's hand and makes the pistol more comfortable to shoot by reducing muzzle rise and allows for faster aim recovery in rapid shooting sequence. The rectangular slide is milled from a single block of ordnance-grade steel using CNC machinery. The barrel and slide are treated with a proprietary nitriding process called Tenifer. The slide and barrel undergo two hardening processes prior to the Tenifer treatment, applied in a 500°C nitrate bath. The Tenifer finish is between 0.4 mm (0.016 in) and 0.5 mm (0.020 in) in thickness, and is characterized by extreme resistance to wear and corrosion; it penetrates the metal, and treated parts have similar properties even below the surface to a certain depth. The Tenifer process produces a matte gray-colored, non-glare surface with a 64 Rockwell C hardness rating (by comparison, an industrial diamond has a rating of 70 HRC) and a 99% resistance to salt water corrosion (which meets or exceeds stainless steel specifications), making the Glock particularly suitable for individuals carrying the pistol concealed as the highly chloride-resistant finish allows the pistol to better endure the effects of perspiration. Glock pistols with their Tenifer treatment are more corrosion-resistant than analogous guns on the market with any other type of finish, including Teflon, bluing, hard chrome plating, phosphates and other alloys. After applying the Tenifer process, a black Parkerized decorative surface finish is applied. The underlaying Tenifer treatment will remain protecting these parts even if the decorative surface finish were to wear off. A current production Glock 17 consists of 34 parts. For maintenance, the pistol disassembles into five main groups: the barrel, slide, frame, magazine, and recoil-spring assembly. The firearm is designed for the NATO-standard 9x19mm Parabellum pistol cartridge, but can use high-power (increased pressure) +P and +P+ ammunition with either full-metal-jacket or jacketed hollow-point projectiles. Standard sighting arrangement of a "first generation" Glock 17 Barrel The hammer-forged barrel has a female type, polygonal rifling with a right-hand twist. The stabilization of the round is not by conventional rifling, using lands and grooves, but rather through a polygonal profile consisting of a series of six interconnected non-circular segments. Each depressed segment within the interior of the barrel is the equivalent of a groove in a conventional barrel. Thus the interior of the barrel consists of six smooth arcs of steel rather than six sharply defined slots. The method by which Glock barrels are rifled is somewhat unusual; instead of using a traditional broaching machine to cut the rifling into the bore, the Glock process involves beating a slowly rotating mandrel through the bore to obtain the hexagonal shape. As a result, the barrel's thickness in the area of each groove is not compromised as with conventional square-cut barrels. This has the advantage of providing a better gas seal around the projectile as the bore has a slightly smaller diameter, which translates into more efficient use of the combustion gases trapped behind the bullet, slightly greater (consistency in) muzzle velocities, increased accuracy and ease of maintenance. Safety Glock pistols are designed with three independent safety mechanisms to prevent accidental discharge. The system, designated "Safe Action" by Glock, consists of an external integrated trigger safety and two automatic internal safeties: a firing pin safety and a drop safety. The external safety is a small inner lever contained in the trigger. Pressing the lever activates the trigger bar and sheet metal connector. The firing pin safety is a solid hardened steel pin that, in the secured state, blocks the firing pin channel (disabling the firing pin in its longitudinal axis). It is pushed upward to release the firing pin for firing only when the trigger is actuated and the safety is pushed up through the backward movement of the trigger bar. The drop safety guides the trigger bar in a ramp that is released only when direct rearward pressure is applied to the trigger. The three safety mechanisms are automatically disengaged one after the other when the trigger is squeezed, and are automatically reactivated when the trigger is released. This passive safety system omits the manipulation of traditional on-off levers, hammers or other external safeties as found in many other handgun designs. In 2003, Glock announced the Internal Locking System (ILS) safety feature. The ILS is a manually activated lock that is located in the back of the pistol's grip. It is cylindrical in design and, according to Glock, each key is unique. When activated, the lock causes a tab to protrude from the rear of the grip giving both a visual and tactile indication as to whether the lock is engaged or not. When activated, the ILS renders the Glock unfireable as well as making it impossible to disassemble. When disengaged, the ILS adds no further safety mechanisms to the Glock pistol. The ILS is available as an option on most Glock pistols. Glock pistols cannot be retrofitted to accommodate the ILS. The lock must be factory built in Austria and shipped as a special order. Feeding The Glock 17 feeds from staggered-column or double stack magazines that have a 17-round capacity (which can be extended to 19 with an optional floor plate) or optional 33-round high capacity magazines. For jurisdictions which restrict magazine capacity to 10 rounds, Glock offers single stack 10-round magazines. The magazines are made of steel and are over-molded with plastic. A steel spring drives a plastic follower. After the last cartridge has been fired, the slide remains open on the slide stop. The slide stop release lever is located on the left side of the frame directly beneath the slide and can be manipulated by the thumb of the shooting hand. Glock magazines are "one-way" interchangeable between models, meaning that a compact or subcompact pistol will accept magazines designed for the larger pistols chambered for the same round. However, magazines designed for compact and subcompact models will not function in larger pistols because they are not tall enough to reach the slide and magazine release. For example, the subcompact Glock 26 will accept magazines from both the full-size Glock 17 and the compact Glock 19, but the Glock 17 will not accept magazines from the smaller Glock 19 or the Glock 26. Sights The Glock 17 has a fixed polymer combat-type sighting arrangement that consists of a ramped front sight and a notched rear sight with white contrast elements painted on for increased acquisition speed—a white dot on the front post and a rectangular border on the rear notch. The rear sight can be adjusted for windage as it has a degree of lateral movement in the dovetail it is mounted in. Three other factory rear sight configurations are available in addition to the standard 6.5 mm (0.26 in) height sight: a lower impact 6.1 mm (0.24 in) sight and two higher impact versions—6.9 mm (0.27 in) and 7.3 mm (0.29 in). Accessories The Glock pistol accessories available from the factory include several devices for tactical illumination, such as a series of front rail mounted "Glock tactical lights" featuring a white tactical light and an optional visible laser sight. An alternate version of the tactical light utilizing an invisible infrared light and laser sight is available, designed to be used with an infrared night vision device. Another lighting accessory is an adapter to mount a flashlight onto the bottom of a magazine. Polymer holsters in various configurations and matching magazine pouches are available. In addition, Glock produces optional triggers, recoil springs, slide stops, magazine release levers, and underwater spring cups. Magazine floor plates (or "+2 baseplates"), which expand the capacity of the standard magazines by 2 rounds are available for models chambered for the 9x19mm Parabellum, .40 S&W, .357 SIG, and .380 ACP cartridges. As alternatives to the standard non-adjustable polymer sight line three alternative sight lines are offered by Glock. These consist of steel, adjustable and self-illuminating tritium night rear sights and factory steel and self-illuminating tritium contrast pointer steel front sights. Variants Following the introduction of the Glock 17, numerous variants and versions have been offered. Variants that differ in caliber, frame, and slide length are identified by different model numbers with the exception of the discontinued Glock 17L. Other changes not dealing with frame and slide length are identified with suffixes, such as "C", which denotes compensated models. Minor options such as frame color, sights, and included accessories are identified by a separate model code on the box and do not appear anywhere on the firearm. Glock pistols come in five form factors, all modeled after the original full-size Glock 17. "Standard" models are designed as full-size duty firearm with a large magazine capacity. "Compact" models are slightly smaller with reduced magazine capacity and lighter weight while maintaining a usable grip length. "Subcompact" models are designed for easier carry being lighter and shorter, and are intended to be used with two fingers on the grip below the trigger guard and do not feature an accessory rail like the larger post generation two Glock models. .45 ACP and 10mm models are slightly larger than smaller cartridge pistols and are available in the sub-compact models Glock 29 (10mm) and Glock 30 (.45ACP). Glock produces a single-stack "Slimline" .45 ACP pistol, the Glock 36. "Competition" versions have longer barrels and slides, adjustable sights, an extended slide and magazine release. Beginning in 2007, Glock introduced several "Short Frame" models designated by the suffix "SF". The short frame was originally designed to compete in the now cancelled U.S. military Joint Combat Pistol trials for a new .45 ACP pistol to replace the M9 pistol. Glock's entry featured an optional ambidextrous magazine release and MIL-STD-1913 rail along with a reduction in the size of the backstrap. The Glock 21SF is currently available in three versions: one with a Picatinny rail and ambidextrous magazine release and two with a Universal Glock rail available with or without the ambidextrous magazine release. Current 10mm and .45 ACP Glock magazines are manufactured with ambidextrous magazine release cutouts. As of January 2009, the Glock 20, 21, 29, and 30 were offered in short-framed variations. These models incorporate a 2.5 mm (.10 inch) reduction in trigger reach, and full-sized models feature a 4 mm (.16 inch) reduction in heel depth. This reduction in heel depth corresponds to an overall reduction in length for those models. 9x19mm Parabellum The Glock 17 is the original 9x19mm Parabellum model, with a standard magazine capacity of 17 rounds. Several modified versions of the Glock 17 have been introduced. The Glock 17C was introduced in 1996 and incorporated slots cut in the barrel and slide to compensate for muzzle rise and recoil. Many other Glock pistols now come with this option, all with a "C" suffix on the slide. The Glock 17L was introduced in 1988 and incorporates a longer slide and extended barrel. Initially, the Glock 17L had three holes in the top of the barrel and a corresponding slot in the slide; however, later production pistols lack the holes in the barrel. The Glock 17L is effectively discontinued and replaced by the Glock 34. The Glock 17MB is a version with ambidextrous magazine catch. The Glock 19 and Glock 21SF are available as MB-variants. The Glock 18, chambered in 9x19mm Parabellum, fitted with a detachable shoulder stock being fired in fully automatic mode The Glock 18 is a selective fire variant of the Glock 17, developed at the request of the Austrian counter-terrorist unit EKO Cobra. This machine pistol-class firearm has a lever-type fire-control selector switch, installed on the serrated portion of the rear left side of the slide. With the selector lever in the bottom position, the pistol will shoot fully automatic, and with the selector lever in the top position, the pistol will fire semi-automatically. The firearm is typically used with an extended 33-round capacity magazine, although other magazines from the Glock 17 will function, with available capacities of 10, 17, or 19 rounds. Early Glock 18 models were ported to reduce muzzle rise during automatic fire. Another compensated variant was produced, known as the Glock 18C. It has a keyhole opening cut into the forward portion of the slide, similar to the opening on the Glock long-slide models, although the Glock 18 has a standard-length slide. The keyhole opening provides an area to allow the four, progressively larger (from back to front) compensator cuts machined into the barrel to vent the propellant gases upwards, affording more control over the rapid-firing machine pistol. The compensator cuts start about halfway back on the top of the barrel. The two rear cuts are narrower than the two front cuts. The slide is hollowed, or dished-out, in a rectangular pattern between the rear of the ejection port and the rear sight. The rate of fire in fully automatic mode is approximately 1,100–1,200 rounds per minute. Most of the other characteristics are equivalent to the Glock 17, although the slide, frame, and certain fire-control parts of the Glock 18 are not interchangeable with other Glock model. The compact Glock 19 in 9x19mm Parabellum The Glock 19 is effectively a reduced-size Glock 17, called the "Compact" by the manufacturer. It was first produced in 1988, primarily for military and law enforcement. The Glock 19 has a barrel and pistol grip that are shorter by approximately 12 mm (0.5 in) compared to the Glock 17 and uses a magazine with a standard capacity of 15 rounds. The pistol is compatible with factory magazines from the Glock 17 and Glock 18, with available capacities of 10, 17, 19, and 33 rounds. To preserve the operational reliability of the short recoil system, the mass of the slide remains the same as in the Glock 17 from which it is derived. With the exception of the slide, frame, barrel, locking block, recoil spring, guide rod, and slide lock spring, all of the other components are interchangeable between the models 17 and 19. The subcompact Glock 26 with tritium night sights in 9x19mm Parabellum The Glock 26 is a 9x19mm "subcompact" variant designed for concealed carry and was introduced in 1995, mainly for the civilian market. It features a smaller frame compared to the Glock 19, with a pistol grip that supports only two fingers, a shorter barrel and slide, and a double-stack magazine with a standard capacity of 10 rounds. A factory magazine with a +2 baseplate gives a capacity of 12 rounds. In addition, factory magazines from the Glock 17, Glock 18, and Glock 19, with capacities of 15, 17, 19, and 33 rounds, will function in the Glock 26. More than simply a "shortened" Glock 19, design of the subcompact Glock 26 required extensive rework of the frame, locking block, and spring assembly that features a dual recoil spring. The Glock 34 is a competition version of the Glock 17. It is similar to its predecessor, the now-discontinued Glock 17L, but with a slightly shorter slide and barrel. It was developed and produced in 1998, and compared to the Glock 17, features a 21 mm (0.8 in) longer barrel and slide. It has an extended magazine release, extended slide stop lever, 20 N (4.5 lbf) trigger pull, and an adjustable rear sight. The top of the slide is milled out, creating a hole designed to reduce front-end muzzle weight to better balance the pistol. The subcompact Glock 29 in 10mm Auto 10mm Auto The Glock 20, introduced in 1991, was developed for the then-growing law enforcement and security forces market for the 10mm Auto. The pistol will handle both full-power as well as reduced "FBI" loads that have reduced muzzle velocity. Due to the longer cartridge and higher pressures, the pistol is slightly larger than the Glock 17, having an approximately 2.5 mm (0.1 in) greater width and 7 mm (0.3 in) greater length. Though many small parts interchange with the Glock 17, with a close to 50% parts commonality, the major assemblies are scaled-up and do not interchange. The standard magazine capacity of the Glock 20 is 15 rounds. In 2009, Glock announced they would offer a 152 mm (6 inch) barrel as a drop-in option. The Glock 29 is a 10mm Auto equivalent of the subcompact Glock 26 introduced in 1997 along with the Glock 30. The pistol features a 96 mm (3.8 in) barrel and a standard magazine capacity of 10 rounds. Like other subcompact Glock pistols, the Glock 29 will function with the factory magazines from its related full-size model, giving an optional capacity of 15 rounds. .45 ACP The slim-frame Glock 36 in .45 ACP The barrels of all .45 ACP Glock pistols feature octagonal polygonal rifling rather than the hexagonal shaped bores used for models in different chamberings. Octagonal rifling provides a better gas seal in relatively large diameter rifled bores, since an octagon resembles a circle more closely than a hexagon. The Glock 21 is a .45 ACP version of the Glock 20 designed primarily for the American market. Compared to the Glock 20 chambered in 10mm Auto, the slide of the Glock 21 is lighter to compensate for the lower-energy .45 ACP cartridge. The standard Glock 21 magazine is of the single-position-feed, staggered-column type with a capacity of 13 rounds. The Glock 30 is a .45 ACP version of the subcompact Glock 29, with a standard magazine capacity of 10 rounds. The factory magazine from the Glock 21, with a capacity of 13 rounds, will function in the Glock

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