The most common sidearm seen in used by the SG teams (although in real life, the M9 is the military designation for the Beretta, the prop weapons used in the show are most likely the civilian Beretta 92FS).
The Heckler & Koch MP5A3, almost exclusively equipped with the Surefire dedicated forend weaponlight, is the primary weapon used by all SG teams for the first few seasons. Then when the main cast and some supporting and extras switched to the P90, the MP5 became less common. Also seen in use by the Free Jaffa Nation later in the series. MP5 also makes a small comeback when we see them again in the hands of a special assault unit raiding a Trust compound. Throughout the series it is generally the case that for non firing scenes the actors carry airsoft replica MP5s with a Navy trigger group, whereas for firing scenes their weapons switch to real firearms with SEF trigger groups.
This assault shotgun is seen mostly in the episodes featuring the Replicators, but actually had its very first appearance in the first episode "Children of the Gods" (Season 1, Episode 1). The USAS-12 shotguns in SG1 are newer CQ versions with a modified carry handle, no front sight and shortened barrel (sometimes with a muzzle brake).
Error creating thumbnail: File missingUSAS-12 auto shotgun in standard configuration - 12 gauge. This version has the 10 round stick magazine. The 20 round drum is most commonly used in the show.
Rifles
Diemaco C7/Olympic K4B
Seen used by Marines, and the security of Stargate Command. These are all Olympic Arms K4B rifles (same receiver style as the Colt Model 715/Diemaco C7), standing in for the M16A2.
The GAU-5/A and GAU-5A/A were the USAF contract versions of the XM177 and XM177E2 "CAR-15" short assault rifle. The USAF Security forces used them until recently, however, most of the non firing GAU-5A/As seen in the show were simply XM177E2 "Airsoft guns". The actual GAU-5A/A carbines look like the XM177E2 but don't have forward Assist buttons.
The GAU-5 variants that appeared on the show seem to be a mix of full-auto converted Colt AR-15 SP1s and Olympic Arms K3Bs, all with chopped barrels and fake GAU-5 flash hiders installed. The converted AR-15 SP1s have the "slab-side" receiver, while the K3Bs are recognizable by their 715-style receiver (forward assist, brass deflector, A1-style rear sight) and "Stowaway" pistol grips.
Error creating thumbnail: File missingXM177E1 Carbine (AKA Colt Model 610) - 5.56x45mm. In USAF service, this weapon was known as the GAU-5/A.Error creating thumbnail: File missingCharles Kawalsky (Jay Acavone) with his Carbine in "The Gamekeeper" (Season 2, Episode 4). This one is a modified Olympic Arms K3B (the "Stowaway" pistol grip is visible if the image is enlarged to full-size).Error creating thumbnail: File missingA Airman in "A Matter of Time" (Season 2, Episode 16) holds one of the fake GAU-5/A.
M16A1
Usually seen carried by the Cheyenne Mountain guards in stock footage. It could also be seen during the lockdown of the mountain in the episode "A Matter of Time" (Season 2, Episode 16).
Contrary to popular belief, there are no real FN Minimi or M249 light machine guns used in Stargate: SG1 or its sister show, Stargate: Atlantis. The light machine guns used by the SG teams are actually Korean-made Daewoo K3s that have been fitted with M249 Paratrooper-style stocks and shortened barrels. Some of the K3s seen on the show also have RIS rails and vertical grips similar to those seen on the Mk 46 Mod 0.
Error creating thumbnail: File missingA Daewoo K3 "Paratrooper" model, with a chopped barrel buttstock removed to resemble an M249 Paratrooper, and with a 200 round "soft pack" magazine. Guns in similar configurations have been seen in many action films. (This picture was edited in GIMP.)Error creating thumbnail: File missingA Marine covers SG-1's advance from the gate in "Show and Tell" (Season 2, Episode 20).
FN M249
Only seen twice, in "A Matter of Time" (Season 2, Episode 16), utilized during the lockdown of the mountain.
Seen attached to M4s and M16s. Prop wise, these were all Cobray 37mm flare launchers meant to mimic the appearance of an M203. What tips them off is the absence of a second trigger, the shape of the trigger guard, the lack of a step up in the receiver, and the cocking lever on the SIDE of the receiver.
Utilized by the SG teams. In a very memorable scene, Jack O'Neill (Richard Dean Anderson) drops two into the shield generator of a Goa´uld mothership in order to disable it during "The Serpent´s Lair" (Season 2, Episode 1).
M67 fragmentation grenadeError creating thumbnail: File missingBra'tac looks on in surprise as O'Neill drops two M67 into the motherships shield generator in "The Serpent's Lair" (Season 2, Episode 1).
Knives
Phrobis M9 bayonet
While not a firearm, an interesting fact is that the knife usually carried by Jack O'Neill (Richard Dean Anderson) is a Phrobis M9 bayonet with an OD Handle and sheath with an integrated pistol mag pouch. The most memorable scene featuring this weapon comes from the episode "Secrets" (Season 2, Episode 9): O'Neill uses it to disable Heru'ur´s Goa'uld hand-device.