Manhunt is the first game in of Rockstar's more controversial franchises. Manhunt has been banned in several countries and implicated by the British media in a UK murder shortly after it's release [to be exact, implicated by the victim's mother; as it turned out, she was so familiar with the game because it was the victim who owned a copy of Manhunt, not his killer].
The following weapons can be seen in the game:
Smith & Wesson Model 586
The Smith & Wesson Model 586 is used by many of the game's characters, and is referred to ingame simply as the "Revolver" (though it is named the ".38 Revolver" in the game's manual). It is often the only handgun available for much of the game. It holds 6 rounds and is reloaded round-by-round rather quickly by ingame characters, which is surprising given that none of them are seen to use speedloaders or similar devices to reload this weapon.
Called a 'Light Handgun' or 'GS Model 23' in the game, the Glock 23 is used in the game by a few gangs (Most notably the "Smileys") and by Lionel Starkweather's (the 'director' who tells you what to do and where to go in the game) personal henchmen. The gun itself is almost a carbon copy of the Glock, with only slight differences in the name and model. For example, the seven slide grooves are now at the front where as the real steel version has them at the back. It is even chambered in .40.
IMI/Magnum Desert Eagle
The Desert Eagle appears as the 'Heavy Handgun' or the more decorative 'Avenger Force .50 AE GS' in the game. It is used in the latter stages of the game by Carcer City SWAT and the Cerberus assault team. Like the Glock, the gun is almost an exact replica of the .50 caliber monster. Subtle differences that can be spotted is that the gun, whilst being chambered in .50 Action Express, holds 9 rounds which is what the .357 version of the Desert Eagle holds.
Powerful up close, the Sawed Off Shotgun is used and seen in many areas of the game. Fires two 12 gauge cartridges. Again the make and model are unclear.
The Franchi SPAS-12 appears as 'Sap 12' or '12-Gauge' in the game. Variants of this gun are carried by the CCPD/SWAT as well as Cerberus with flashlights attached.
Enfield L42A1/Enfield Enforcer
Used in only a few missions, the Enfield L42A1/Enfield Enforcer fires 7.62mm ammunition with a six shot capacity. The gun appears to be bolt-action and very accurate. Its ingame name is simply "Sniper Rifle" but the manual's name for it is "IDK Type 2 Sniper."
A mash-up of a Uzi and a MAC-10, this fictional weapon has good range and fair accuracy, as well as a high rate of fire. It is referred to simply as a "Sub-Machine Gun" ingame, as well as the "Spaz Mark 1" in the game's manual. This SMG is primarily carried by CCPD officers and SWAT personnel in the game, and it is also seen in the hands of what appear to be "The Skinz" as shown in the promotional picture below.
The M16A2 is called the 'Defender Mark 1', the gun can be fired in semi or fully automatic. The gun also features a shortened barrel and high power. 2-3 shots to the body will kill, where as a shot to the head will remove most of it entirely. Also, the gun holds 30 rounds despite being fitted with a 20 round magazine. Only seen in the last few levels of the game in the hands of Cerberus agents.
While technically not a firearm, it is the most nonviolent way to subdue an enemy. It is used in only a few missions. The gun fires .50 caliber Ketamine shots, enough of a dosage to make Mike Tyson fall asleep.
Heckler & Koch PSG-1
The PSG-1 was to appear as a second sniper rifle, but was removed before the final release.