The following weapons appear in the video game Half-Life and its expansions:
The Glock 17 is the standard issue sidearm of the Black Mesa security guards. It has a 17 round magazine capacity and is accurate, but not particularly powerful. A suppressed version is used by the female Black Ops, and HECU (Hazardous Environment Combat Unit) medics are also seen using the pistol in the Opposing Force expansion pack. The Glock (and the 92FS in the HD pack) can fire underwater.
The High Definition pack replaces the Glock 17 with the Beretta 92FS. The change is purely aesthetic, and changes none of the weapon's stats. Although 17-round magazines are possible on a real Beretta 92FS, these ones have a deeper base than the one on the 15-round model in the game, and were not in existence when the HD pack was released.
The stainless .357 Magnum Colt Python is found mid-way through the game at the bottom of a blast pit and is far more powerful than the 9mm pistol, but has a smaller capacity and lower rate of fire. Reloading is done with the help of a speedloader, but it is still slower than the pistol's.
In the multiplayer part of the game, the Colt Python is additionally equipped with a laser pointer under the barrel. This enables the player to use a zoom function, which acts as the secondary fire mode.
Desert Eagle Mark XIX
The Desert Eagle Mark XIX appears only in the Opposing Force expansion pack as the standard-issue sidearm of the U.S. Marines. The weapon is also seen used at times by Black Mesa security guards. The Desert Eagle has an attached LAM (Laser Aiming Module), which can be turned on and off using the secondary fire key. Strangely enough, the iron sights are removed from the first person model (whereas the world model appears to have them), which would make any sort of aiming with it difficult in real life unless using the LAM (sure enough, the weapon in-game is quite inaccurate when fired without the LAM active). Another modeling error is that the third person model is strangely short, with the slide and barrel measuring about two-thirds the length of an actual Desert Eagle.
In Opposing Force, the Desert Eagle replaces the Colt Python. It uses .357 Magnum ammunition (the game manual also refers to it as "Desert Eagle .357"), but holds only 7 rounds while its real life .357 Magnum counterpart has a capacity of 9 rounds. This reveals another final (though more minor) modeling error - The lack of barrel fluting which is present on actual .357 variants of the Mark XIX Desert Eagle (The .50 AE variant, which is more commonly seen in films and television, lacks the fluted barrel). The weapon is very out of place since the Marines have never used the Desert Eagle as their sidearm throughout their history.
The SPAS-12 shotgun is found in some armories in the facility and is also used by some HECU Marines. Strangely, it has the unrealistic ability to fire two shells at once (alternative fire), instead of firing in semi-auto like the real SPAS-12. Seemingly the developers believed the weapon's magazine tube was a second barrel.
Note of interest: The icon for the weapon in the original game's selection screen displays an Ithaca 37 "Stakeout" shotgun.
Heckler & Koch MP5SD3
The Heckler & Koch MP5SD3 is the primary automatic weapon in the game and is the HECU's standard issue weapon. It features a retractable stock, incorrectly holds 50 rounds in a 30-round magazine, and has M203PI grenade launcher. Since it uses the same ammunition, the MP5 shares its ammo pool with the Glock 17. As seen in early gameplay videos, it was originally suppressed as the first person model would suggest. Interestingly, in the config file it is listed as weapon_9mmAR, whereas it is actually a submachine gun.
Heckler & Koch MP5A3
The world-model of the SD3, and the submachine guns used by the Marines are replaced with Heckler & Koch MP5A3s. (The inventory icon of the MP5SD3 is also an A3 model, but it strangely has a AR-15-style front sight.)
Colt Model 727
The High Definition pack replaces the MP5 with the Colt Model 727, denoted by its M16A2-style rear sights and integrated non-detachable carry handle. The M727 would appear to be more realistic, but it still shoots 9mm rounds and it is still mainly used in close quarters like an SMG. In the Playstation 2 version of the game, the M727 has a separate ammo supply and enemies tend to avoid close quarters with it.
FN M249E2 SAW
The FN M249E2 SAW machine gun appears only in the Opposing Force expansion pack. It is far the most powerful non-fictional weapon, with high damage, range and moderate accuracy. It should be noted that the belt box carries only 50 rounds whereas its real-life counterpart carries 100 or 200. Interestingly enough, the recoil is so powerful that Cpl. Shephard slides backwards if he fires it continuously.
The M40A1 Sniper Rifle appears only in the Opposing Force expansion pack as a usable weapon, where it replaces the Crossbow. It is incorrectly depicted to have a detachable box magazine, whereas the real M40A1 has an integral magazine. Other variants of the Remington 700 have a detachable box magazine; note that ten years after the game's release, the updated M40A5 was produced, having the 5-round detachable box magazine. Also, due to an oversight, the character only pulls back the bolt before each shot and pulls it back then forward before reloading an empty magazine. A fixed model that makes the weapon operate correctly can be found on GameBanana.
M203 Grenade Launcher
The M203 grenade launcher is attached to the MP5 (and the Colt M727 in the High Definition expansion pack). The MP5 uses the the M203PI variant, whereas the M727 uses the full-length M203. In-game it can carry a maximum of 10 rounds, and is never seen reloading or possessing a trigger mechanism of any kind. The 40mm grenades it fires apparently had their fuses removed, since in real life grenades need to travel for around 30 feet before arming. They also arc extremely fast and tumble end over end while in flight. The M203 is not capable of being mounted on an unmodified MP5 in real life.
Referred to as the "GAM14B". The in-game model is a more futuristic version of the Armbrust ATW. It is shown as being reloadable and laser-guided.
Mk 2 hand grenade
The Mk 2 hand grenade is the standard grenade used by the Marines, and apparently kept in large numbers by security guards (though they never use it). Strangely, instead of rolling to a stop after it is thrown, it simply bounces a few inches then stays there until it explodes. The spoon also stays on when the grenade is thrown, due to an oversight on the part of the developers. This grenade was discontinued from active use by the time of the Vietnam War, making it well obsolete for the period in which the game takes place.
Satchel Charges act as command-detonated bombs with very high damage and blast radius.
The Browning M2HB appears as a usable emplaced weapon throughout all the games. It is mostly seen mounted on tripods, but sometimes on pintle mounts and tanks. The M2HBs have unlimited ammunition, and are used pretty often by the "Opposing Force".
M230 Chain Gun
U.S.M.C. and Black Ops Apache helicopters are armed with M230 Chain Guns.
The M202 FLASH appears in the form of an emplaced rocket turret with some sort of magazine mounted on the side for bigger capacity. OpFor soldiers use it the original game. This turret cannot be used by Gordon.
Bushmaster M242 Chain Gun
The M242 Bushmaster Chain Gun is seen mounted on several Bradley IFVs.
The BGM-71 TOW is also seen mounted on the Bradley IFVs. Interestingly, some Bradley's use only the M242 Chain Gun when the player makes contact with them, while others fire only the TOW.