Stargate SG-1

Pistols

Beretta M9

The standard sidearm for U.S. military personnel.

Sub-machineguns

FN P90 Personal Defense Weapon

This became the most common weapon after its introduction in Season 4, Episode 8 ("The First Ones").

H&K MP5A3

The main weapon used by all SG teams for the first few seasons.

Heckler & Koch MP5A3 - 9x19mm

Shotguns

Aserma Protecta Shotgun

This was portrayed as a grenade launcher.

Franchi SPAS 12

Franchi SPAS-12 shotgun - 12 gauge

Carbines and Rifles

GAU-5/A

The GAU-5/A was the USAF contract version of the XM177 "CAR-15" short assault rifle. The USAF Security forces used them until recently, however, most of the non firing GAU-5/As seen in the show were simply XM177E2 "Airsoft guns". The actual GAU-5/A carbines look like the XM177E2 but don't have forward Assist buttons.

"Carter Special" Micro Carbine

This is a customized Armalite M15A4 Carbine with a short 11.5" barrel, aftermarket quadruple-rail SOPMOD accessory forend, and a modified thumb-hole stock taken from a Sterling AR-180 rifle. It is used with an ELCAN sight and a Beta C-Mag dual-lobed 100-round drum and can mount a vertical foregrip and a side-mounted flashlight on the accessory rail. It first appears in Season 7, Episode 9 ("Avenger 2.0"). It gets its name from Major Samantha Carter, the only character who carries it.

Heavy Weapons

M72 LAW

M72A2 LAW (Light Anti-armor Weapon) - 72mm

Cobray 37mm Launcher

CM79LF 37mm Launcher

O'Neill uses a CM79LF as a 40mm grenade launcher.

AT-4

M136 AT4 Rocket Launcher - 84mm

Most commonly 'mis used' as a surface to air missile to shoot down Goa'uld Death Gliders, however, the AT-4 is an 84mm Anti Tank Weapon.

G36K

Several times in the last couple season, this rifle was seen in used by the Marines or Mitchel

H&K MP-7

Seen in a few episodes in place of the famous P90 the team uses. Teal'c has been used duel wielding these in an episode or 2.