Left 4 Dead
The following weapons appear in the game Left 4 Dead:
Springfield Armory M1911-A1
The Springfield Armory M1911-A1 is the backup handgun for the survivors. A second one can be found randomly in-game and dual-wielded, though the second will lack an attached flashlight. Though they have some modern modifications added, like an extended thumb safety, beaver-tail grip-saftey, trigger with cut-outs, checkered front-strip, and Colt Commander ring-hammer, they keep the small and mediocre sights of the original M1911A1.
These 1911-A1s hold 15 rounds in their magazines even though the magazines being loaded into them are standard single-stack magazines that, at most, have 8 rounds of.45 ACP that the ingame model claims they're chambered in (see screenshot below), and they have an unlimited ammo reserve.
High Standard Model K-1200
The shotgun seems to be modeled squarely from a High Standard Model K-1200 Riot Deluxe Model, but has the trigger guard of a Remington Model 870 Shotgun and an Ithaca 37 magazine tube end is a first tier weapon. Francis uses this weapon in the intro cinematic and during the game. The receiver has the fictional make of the shotgun named as "Renegade Rangemaster". It should noted that the developers meant it to be an ambiguous pump-action shotgun.
A full-sized Uzi submachine gun is a first tier weapon with a 50-round capacity (even though it's modeled with a 32-round magazine) and a flashlight tacked on its handguard is available to the survivors. It's also Louis' main weapon in the opening cinematic.
Benelli M4 Super 90
The Benelli M4 Super 90 is a second tier weapon with a 10-round magazine (which would require an extended magazine tube; the in-game weapon is modeled with the civilian legal 4-shot tube) and a flashlight clipped to the sling loop on the fore-end. Francis will always use it whenever he finds one.
The M16A2 is a second tier weapon with a 50-round magazine (Modeled after a standard 30-round magazine) and a flashlight clipped to its foregrip.
The weapon in the game is fully automatic, though the real M16A2 fires only in semi auto and 3-round bursts as it's the A1 or A3 that's full-auto capable. This suggests that the weapon is an M16A2 with an M16A1 lower receiver though is says M16A2 on the lower receiver. It's Bill's main weapon in the intro cinematic, and both Bill and Louis will pick them up if they find them during the game.
Ruger Mini-14 Ranch Rifle
The Ruger Mini-14 Ranch Rifle is a second tier gun with a magazine capacity of 15 rounds in a 10-round magazine. The stock design suggests that its a pre-2005 model. Strangely enough, the Rifle combines the old, single-bladed front sight with a John Masen flash-hider and the post-2005 aperture rear sight. It's Zoey's preferred gun in the game. It should also be noted that despite being referred to as the "Hunting Rifle" in-game, it was illegal to hunt with a semi-auto rifle in Pennsylvania at the time of the game's release and setting; this law was later changed.
GE M134 Minigun
A GE M134 Minigun, mounted on a monopod and set up behind sandbags, is usually found at the end of a campaign. It shreds almost all infected to pieces in seconds.
Despite its multi-barrel operation design to prevent this, it overheats rapidly with the barrel cluster turning red hot after only a few seconds of continuous fire, presumably for game balance reasons. It appears to be rendered with a 200-round ammo can which would empty in four seconds in real life, in game however, it has infinite ammo and doesn't need to be reloaded.
The spade grips are mounted higher than normal in relation to the gun because they are attached to the same custom frame used for the Terminator 2 and Predator handheld Miniguns (minus the chainsaw grip/M60 handguard), rather than an actual Minigun mount.
(Art) Custom HK MP5
The Heckler & Koch MP5 with a railed handguard with rail covers, a flash hider, an Aimpoint CompM2 sight, a Navy trigger group, and a folded PDW stock appears in most loading posters and several wallpapers/concept arts in the hands of Bill and Louis (Francis has the Mk. 18 instead, which would later be used in the posters for the sequel). Interestingly, a scrapped Counter-Strike: Global Offensive MP5 model also had a railed handguard with covers and a flash hider, but it was fitted with a normal A3 stock and S-E-F trigger group.