The Type 77 is the starting handgun in game. It is chrome plated. Used by JD and as a sidearm by the Fortieth Day Initiative mercenary army.
Converted Glock 17
The Glock 18 is in fact a converted Glock 17, as it lacks the slide-mounted selector switch. It can be customized with a 33 round magazine.
Desert Eagle Mark VII
The Desert Eagle MK VII is labeled as a .44 in the game. It starts with a eight round magazine, but can be upgraded to 12 rounds. Capable of blowing an enemy's head off in one shot. It is the sidearm of Breznev.
The TDI Vector in the game is referred as the "TD-V 0.45 SMG" and it costs $35,000.
QCW-05
The QCQ-05 appears in the game as the "Type 05 SMG".
FN P90
After saving civilians in Chapter 3, the FN P90 is unlocked.
Assault Rifles
Heckler & Koch G36C
Rios and Salem start with Heckler & Koch G36Cs. It is also used by FDI mercenaries early in the game and can be picked up from them. JD also carries one. Can be modded into an MG36.
FAMAS F1
The FAMAS F1 is referred to as the "FELIN-2C". Although shown carrying an AK in cutscenes, Brezhnev uses this as his standard weapon.
The Hawk Semi-Auto shotgun is available as "HM Shotgun" depending on the choices the player makes.
AA-12
The AA-12 is available for purchase. The 20-round drum is available for purchase later.
Machine Guns
M249 SAW
A hybrid M249 SAW is available for purchase. The stock gun comes with the fixed stock of a full-sized M249, but with the short barrel of a M249 Para, as well as the ammo bag of a M249 Para. The M249 E1 barrel, 120-round ammo box, and Para telescoping stock are available upgrades.
XM312
The turret weapon encountered throughout the campaign.
General Dynamics GAU-19/A
The General Dynamics GAU-19/A is used by the FDI machine gun heavy. Once the heavy is defeated, the player can pick it up.
Grenades/Grenade Launchers
M32 MGL
The M32 MGL is available to the players as the "MK Grenade Launcher." Used by grenadier FDI heavies.
M203 grenade launcher
The M203 grenade launcher is available as a front mount attachment as "M203 40mm GL."
RPG-7
The RPG-7 is available for purchase. Like in the first game, there's no way to customize it other than paint scheme. Used extensively by FDI mercenaries.
M67 Grenade
The grenades available in-game
Fan Designs
AS-KR1
The American winners of the Army of Two design contest created the AS-KR1. They were members of a website called The Angry Joe Show and call themselves the Angry Joe Army. Design was drawn up by internet artist Marobot.
Chambered in 7.62 X 39mm with enhanced accuracy due to the built in ranged scope. The weapon comes with an underslung shotgun that can chamber regular shotgun shells, airburst shells, and less lethal tazer shells (supposedly to imitate the webshow hosts chain lightning ability).
The developers of Army of Two: The 40th Day held a gun design contest in which the winners will have their guns put into the game. One of the winners was the Grand Pinger, designed by members on an online image board called OPERATORchan. The rifle's name is derived from the M1 Garand and the distinctive sound that is made when a clip is ejected. The gun is a modified Mosin-Nagant with a shotgun stock, backwards mounted SVD magazine, Eotech along with a backwards mounted ACOG. It also features a backwards vertical grip, a paintball gun hopper, a backwards laser sight, a backwards flashlight, and a small suppressor. The final product, while retaining many features of the original, has been modified. It was entered as a joke, with a description describing it as "designed by Mack of FutureWeapons".