During the attack on his home that results in Jenny (Alyssa Milano)'s kidnapping, John Matrix (Arnold Schwarzenegger) retrieves a Heckler & Koch HK91 from his tool shed to fend off the attackers. Since the receiver has only two fire positions (Safe and Fire) it is the semi automatic HK91 rather than the select fire G3.
Beretta 92SB
Matrix (Arnold Schwarzenegger) is also seen taking a Beretta 92SB from his tool shed and tucks it in his belt. He never gets to use it though and it dissapears from his belt when he crashes his car.
The original M16 (also known as the Colt SP1 rifle) is used, as denoted by the slab side upper receiver. The three pronged flash hider, however, is replaced with a standard A1 birdcage flash hider in many of the rifles.
South American police are seen with M16 (Colt SP1) rifles outfitted with A2 handguards to look like M16A2. Kirby's men at the end of the film are also seen with these rifles.
Obvious because the MGC M16 (Model Gun Corp of Japan) metal M16 replicas have three pronged flash hiders, but they are mounted upside down and their 20 round magazines are blued, not Colt anodyzed gray. Used by every soldier/combatant carrying an M16 when they are doing stunts or pointing the muzzle directing at someone without firing. The replicas were probably used so extensively for safety purposes.
There are numerous appearances of M16A1 rifles in the film; used by U.S. military personnel as well as some of Arius (Dan Hedaya)'s men, one of which Matrix commandeers and uses as well. Most of the M16 rifles seen have 20 round magazines, but some have 30 round magazines. Throughout the final battle, the rifles in the hands of actors and stuntmen change from original M16 (SP1) rifles to M16A1 rifles and back again.
General Kirby's men, who are assigned to protect Matrix and his daughter, but end up killed themselves are armed with CAR-15 carbines. Not XM177s/Colt Commandos, they look to be commercial CAR-15 clones due to the length and shape of their 'fake' XM177 suppressor/flash hider.
Arius' men use Ruger Mini-14 GBs with factory folding stocks. Several of them are seen firing at Matrix and a few are seen dying with their Ruger Rifles. Some are stainless steel models, others are blued models.
Heckler & Koch HK94 (chopped & converted)
One of Arius' men is seen firing a Heckler & Koch HK94 with the 16" barrel chopped down and converted to full auto to resemble an MP5A3. The only featture seen to note this is the lack of the three barrel lugs on the barrel.
One of the weapons used by Matrix during the assault on Arius' base, the Valmet M78 is a Finnish light machine gun similar in appearance to the RPK, the main difference being a different muzzle brake, front sight assembly, and many other structural differences. The Valmet M78 Light Machine Gun has a standard RPK 'style' buttstock. The later Valmet M78/83 has a synthetic thumbhole "Dragunov Style" stock. This is the version used in the film. The Valmet M78 series of Light Machine guns came in 7.62x51mm (.308) and 7.62x39mm calibers.
Another weapon used by Matrix during the final assault, the M202A1 FLASH is the 4-barreled rocket launcher first seen being used by Cindy (Rae Dawn Chong) to flip the police van carrying Matrix after he's arrested raiding a sporting goods store for supplies.
One of the weapons used by Matrix that appears in the the final assault is the full size Uzi, when when stealing the seaplane to reach Arius' compound and during the final battle.
A Remington 870 shotgun is used by Matrix during the final raid on Arius' compound. The gun has a long barrel and a high-capacity magazine tube. However, in the film, the shotgun actually changes (continuity error) several times in the sequence, sometimes the foregrip looks different and the sling changes from being slung over the barrel to over the magazine tube. Since the movie had many continuity errors with the other guns, it makes being 100% sure of the shotgun type difficult.
A Steyr AUG is seen on the wall of the hidden arms room in the 'surplus store', but never used. Seen again, during the final raid on Arius' compound, Arius attempts to take out Matrix using a Steyr AUG bullpup rifle, but ultimately fails and ends up among Matrix's body count.
Another weapon Matrix uses during the final battle is a chrome Desert Eagle chambered in .357 or .44 being that the film was shot in 1984 and released in 1985.
The M60E3 machine gun first appears being used by one of Arius' men, and is commandeered and used by Matrix. The M60E3 used in the film had a shorter barrel, several inches shorter than the standard M60E3.
Just before starting the final battle, Matrix plants several M18A1 Claymore anti-personnel mines on the grounds of the complex, and triggers it remotely during the battle. Though the M18A1 Claymore is an antipersonnel mine, the ones in the film are strong enough to vaporize an entire building, indicative of the 'exaggeration' of Hollywood movies. The M18A1 Claymore mines are not real (of course NONE are real in movies), however the ones in this film are even more 'customized' than usual. They are plastic casts of the M18A1 and fabricated to take an internal Radio receiver (and custom detonator). The Real M18A1 would be a self enclosed unit, two plastic halves enclosing the explosive and steel balls (shrapnel), and would not have room to add on an internal radio unit.