Thomas Murphy (Kevin Costner) carries a pair of M1911A1s which he wields akimbo during the Casino heist. At one point in the movie, he loses these guns after being arrested, and later receives a replacement from his friend Jack (Howie Long).
During one scene of the Casino Heist, a Las Vegas Police Officer attacks Murphy and Michael's group with a SIG P226 which briefly changes to an M1911A1.
Gus (David Arquette) uses a Smith & Wesson Model 29 during the Casino heist. He tries to reload the weapon during the firefight, but seems to give up and uses his assault rifle instead.
Just before the warehouse shootout, Jack (Howie Long) is seen loading a Smith & Wesson Model 686. Michael (Kurt Russell) catches Jack off guard and disarms him. He holds the weapon to Jack and Murphy (Kevin Costner) until SWAT shows up and he drops the weapon.
Franklin (Bokeem Woodbine) uses a Beretta M93R during the Casino heist. The weapon appears to be converted to full auto, and Franklin fires it with no concern of innocent bystanders.
When the group retreats to the elevator, a Las Vegas Police Officer orders the group to stop and then attacks them with a SIG P226. He shoots Franklin (Bokeem Woodbine) several times before Murphy (Kevin Costner) disarms him and shoots him in the head.
Near the end of the movie, Jack briefly draws his own SIG P226 when Michael and Murphy have their standoff in the warehouse.
Michael carries a Smith & Wesson 5946 which he uses to threaten Cybil (Courtney Cox) after she refuses to hand over her car. (Hey, he already gave her a big wad of cash, what else is he gonna do?)
Murphy gets pulled over by an officer carrying a Single Action Army, which he uses when he challenges Murphy to a quick draw duel.
The front sight has been filed off for a faster draw. The guy playing this sheriff is a quickdraw shooter, and removing the front sights is a pro technique if you can quick draw for real. - Gunmaster45
The lack of a firing pin on the hammer means the revolver has a transfer bar safety and is likely a Ruger Vaquero. This is a very popular revolver to be modified for quick draw competition.
Looks like a chrome/Stainless Beretta 92 to me, going by the slide design and front of trigger guard.
Shotguns
Franchi SPAS 12
Murphy's (Kevin Costner) main weapon during the Casino heist is the Italian Franchi SPAS 12 shotgun. He kills several security guards, reloads mid fight, and proceeds to kill several more guards before discarding the weapon due to it's long reload time.
Just before the final shoot out in the warehouse, Murphy (Kevin Costner) is given a short barreled Mossberg 500 with rear and forward pistol grips. He uses the weapon to shoot Michael (Kurt Russell) after SWAT shows up, and briefly uses it to shoot at the SWAT team members.
Hamilton (Ice-T) uses a pair of FN P90s wielded akimbo during the warehouse shoot out. In one of the more cool looking (and kind of stupid) scenes, Hamilton rides a zip line upside down, spraying both FN P90s at the SWAT officers. He is quickly gunned down, of course, for exposing himself as such an easy target.
The casino security guards as well as Pit Boss #1 (Paul Anka) are, just like himself, armed with Ruger Mini-14s during the closing scenes of the Casino Heist. Two of the guards exchange fire with Murphy and Michael's group as the retreat to their getaway helicopter.
During the casino heist, Gus (David Arquette) and Franklin (Bokeem Woodbine) use strange-looking compact assault rifles. One of these weapons is also used near the end of the movie, when Murphy (Kevin Costner) uses one for the first part of the warehouse shoot out. These weapons are custom-built Rocky Mountain Arms Patriot Pistol "carbines". They were clearly built by fitting Patriot Pistol upper receiver/barrel assembles to the lower receiver/telescoping stocks of some other M16 carbine variants, mostly likely the XM177 or Model 654. The armorers then added M4-style carry handles and 100-round Beta-C magazines. Guns similar to these have also been seen in Congo and Soldier (coincidentally, the latter is another movie that starred Kurt Russell).
Hanson (Christian Slater) and Michael (Kurt Russell) use M16 carbine variants that are mocked up to resemble Colt XM177 during the the casino heist. Michael never fires his weapon at any of the security guards, instead shooting the glass above a group of pursuing guards. Michael then passes his gun to Murphy (Kevin Costner) as the group makes their escape to the helicopter.
All of these rifles are fake XM177 rifles which seem to have been built from other AR variants. The real XM177 has a slab-side receiver, which only Michael's gun has (at least when he's in the elevator). The rifles used by the other robbers have both M16A2-style receivers (forward assist, brass deflector, and M16A2-style rear sight) and Model 715-style receivers (forward assist, brass deflector, and M16A1-style rear sight). This means that they're probably other AR carbine variants with chopped barrels and fake XM177 flash hiders fitted. Most of the Hollywood "XM177s" seen in movies are just like these (see also The Rock, for instance).
Daewoo K3 (visually modified to resemble M249 Paratrooper SAW)
During the final shoot out in the warehouse, Jack (Howie Long) uses a light machine gun which may appear to resemble an M249 Paratrooper SAW against several SWAT officers. However, this weapon is actually a Daewoo K3 that was visually modified to resemble an M249; this is discerned most easily by looking at the front sight After Jack is gunned down while trying to save Murphy (Kevin Costner), Murphy picks up the K3 and uses it for his last stand.
Near the end of the Casino shoot out, an LVMPD officer tries to stop Michael and Murphy's group when they retreat to the elevator. The officer's weapon changes briefly from a SIG P226 to a M1911.
Error creating thumbnail: File missingWhen the officer shoves his gun between the elevator doors, the gun is a SIG P226 (see insert). When there's a close up of the gun firing, it's a M1911.
Winchester Model 1894
After Murphy betrays Michael, a trucker find him on the road and offers him a ride. Behind the trucker is Winchester Model 1894.
