The 9x19mm 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 it 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, not even the (now incorrect) magazine capacity. It replaces every Glock 17, except for the suppressed ones used by the female Black Ops assassins.
The .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.
The Desert Eagle Mark XIX appears only in the Opposing Force expansion pack as the standard-issue sidearm of the U.S. Marines. The Desert Eagle has a attached LAM (Laser Aiming Module), which can be turned on and off using the secondary fire key. Strangely enough, the iron sights are removed, which would make any sort of aiming with it difficult in real life unless using the LAM. Another modeling error is that the w_model is strangely short, measuring about two-thirds the size 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. It's also very out of place since the Marines have never used the Desert Eagle as their sidearm throughout their history. They've only used the M1911/M1911A1 in .45 ACP and the M9 in 9mm.
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.
The H&K 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. The weapon should actually be suppressed, but is not. Interestingly, in the config file it is listed as weapon_9mmAR, whereas it is actually a submachine gun.
The world-model of the SD3, and the submachine guns used by the Marines are actually MP5A3s. (The inventory icon of the MP5SD3 is also an A3 model, but it strangely has a AR-15-style front sight.)
The High Definition pack replaces the MP5 with the Colt Model 727, denoted by its A2-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.
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 drum magazine carries only 50 rounds whereas its real-life counterpart carries up to 100 or more. 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 an usable weapon, where it replaces the Crossbow. It is incorrectly depicted to have a 5-round box magazine, whereas the real M40A1 has an integral magazine. The updated M40A5 is the variant that has the 5-round box magazine.
The M203 grenade launcher is attached to the MP5 (and the Colt M727 in the High Definition expansion pack.) 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.
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 (Not to mention this grenade was discontinued during the Vietnam war).
The Browning M2HB appears as a usable emplaced weapon throughout all the games. It is mostly seen mounted on tripods, but sometimes on monopods and tanks. The Brownings have unlimited ammunition, and are used pretty often by the "Opposing Force".
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.
The BGM-71 TOW is also seen mounted on the Bradley IFV's. Interestingly, some Bradley's use only the M242 Chain Gun when the player makes contact with them, while others fire only the TOW.
