The Semi-Automatic Assault Shotgun is a powerful pump-action shotgun that fires buckshot in a cone-shaped pattern. Primarily used by the HECU, it is used by all playable characters from the Half-Life games' story arc.
- The shotgun has two fire modes. The first fire mode fires four pellets with a medium-sized spread, uses one shell and has a small delay between shots, while the alternate fire mode fires eight pellets in a larger, more loose spread and uses two shells, but has a longer delay between shots.
- The shotgun is reloaded one shell at a time. The reloading process can be interrupted at anytime by pressing the fire key.
- The weapon is commonly used by the HECU, who often have one or two soldiers armed with shotguns mixed with ones wielding Submachine Guns.
- In Half-Life, the shotgun is first acquired in the game's fourth chapter, Office Complex, at the end of a hallway. If not found there, it can be found scattered throughout the rest of the chapter.
- After Freeman is captured and his weapons are confiscated, the shotgun can be obtained by killing a shotgun wielding HECU soldier at the start of the chapter Questionable Ethics.
- The shotgun's primary fire is very effective against weak enemies, such as Headcrabs, Zombies, and Vortigaunts. However, the primary fire mode falters against stronger enemies, such as the Bullsquid, because of the low damage output and the small delay between shots.
- The shotgun's alternate fire is one of the most powerful attacks the player can use. In Normal mode, it can kill any enemy up to an HECU soldier in one hit, as long as around six pellets connect. The alternate fire also does heavy damage against the Alien Grunt, but the long delay between shots makes the player very vulnerable to counterattacks, especially while being close to the enemy.
- The only enemy that the shotgun does poorly against is the Alien Controller. At the various ranges the Alien Controller can be at, most of the shotgun's pellets will miss the creature due to its spread, no matter what firing mode is used.
- The shotgun ammo being very common, it is unlikely to run out of ammo for it throughout the game.
- Reloading must be made as often as possible, as an empty shotgun magazine takes much longer to reload than other weapons.
- In deathmatch gameplay, one shot only fires two-thirds bullets, but each bullet causes four times as much damage.
 Behind the scenes
Early footage showed that the shotgun had a completely different skin that was white. All traces of the old skin were removed except for the shotgun used by the scientist at Sector F's Level A, which still uses that old skin. However, when the scientist puts the shotgun down, its skin reverts to the final one.
- The shotgun, along with its Half-Life 2 counterpart, is inspired by the real-world SPAS-12 by Franchi. The weapon icon in the HUD depicts a different model of shotgun, inspired by the Ithaca 37). The Half-Life High Definition Pack remedies this by replacing the icon and making it look like a real SPAS-12.
- Although the shotgun can switch between pump-action and semi-automatic modes, only the player uses the pump-action, while the HECU uses the semi-automatic. It is impossible to switch modes in-game. Moreover, in the Half-Life: Source, soldier can fire his shotgun much faster then they did in GoldSrc version of Half-Life, along with his Submachine Gun. However to compensate this, the shotgun deals sightly less damage, in Half-Life two close range shot is powerful enough to kill a Security Guard while in the Source verion, is require four shot to kill.
- In Half-Life: Source, it possible to skip the pumping animation and increase the rate of fire by quickly pressing the quick switch key after each shot.
- When the shotgun is used by HECU, they will reload all shell at once instead of putting one shell at a time.
The shotgun scientist and a security guard before seeing Gordon, mirrored in Half-Life 2.
 List of appearances
- Half-Life: Day One (First appearance)
- Half-Life: Uplink (Non-canonical appearance)
- Half-Life: Opposing Force
- Half-Life: Blue Shift
- Half-Life: Decay
- Half-Life 2: Raising the Bar