Sergeant Tom O'Meara's (Harrison Ford's) service sidearm is a Smith & Wesson Model 10 Heavy Barrel with some type of rubber grip. One of these revolvers is also used by the Loyalist gunman who murders Frankie Maguire's father in 1972, when he is still a boy.
A Norinco Type 56-1 (Chinese AKS-47/AKMS) assault rifle is used by Frankie Maguire (Brad Pitt) during the opening gun battle in Belfast between the British Army and Maguire's Provisional I.R.A. Active Service Unit.
An M16A1 is used by the Provisional IRA Volounteer "Desmond" (David Wilmott) during the gun battle in Belfast. Another is used by one of Billy Burke's (Treat Williams') men during the scene where Frankie Maguire confronts him.
The SAS operators who attempt to apprehend Frankie Maguire and his crew are all armed with Heckler & Koch MP5A3 submachine guns. For some reason, the MP5s all have the older-style "slimline" forearm when the SAS men are in their car loading their weapons, but when the shootout begins, the MP5s all suddenly have the newer "tropical"/wide-type forearm.
When the shootout in Belfast ends, the Mi-5 agent Harry Sloan (Simon Jones) kills "Desmond" (David Wilmott) with a Heckler & Koch P7M8 pistol after Desmond refuses to tell him where Frankie Maguire is hiding.
When Frankie Maguire (Brad Pitt) is visited in hiding by another IRA member, he comes out of his hiding spot brandishing a SIG-Sauer pistol of some type, most likely a SIG-Sauer P226.
When Frankie Maguire comes to America under the alias Rory Devaney, he takes along a Browning BDA 380 pistol, which he hides in the same bag with the money needed to purchase the Stinger missiles.
Tom O'Meara also carries a Smith and Wesson model 36 as his backup weapon. At one point, Frankie Maguire takes this revolver from Tom and uses it in the later part of the movie.
A sawed-off Remington Model 31 shotgun is used by one of the thugs whom Burke sends to Tom O'Meara's house to look for the money that Maguire owes him.
A pistol-grip, short-barrled Ithaca 37 is used by one of Billy Burke's men when Frankie Maguire goes to the warehouse to get the missiles from them. Maguire himself also winds up using this shotgun to kill several of Burke's men.
After Frankie kills several of his men, Billy Burke (Treat Williams) dives into his car and comes out with a Ruger KP94 pistol, which he uses to shoot at Frankie.
The movie revolves around a plot by the IRA to acquire FIM-92A Stinger surface-to-air missiles, for which Frankie Maguire (Brad Pitt) is sent to the U.S. to make the purchase from arms dealer Billy Burke (Treat Williams). However, no Stingers ever appear on-screen during the entirety of the film (even though the trailer featured stock footage of a Stinger launcher being used). The only glimpse of the missiles that the viewers ever see are the cases which (allegedly) contain them, as seen below:
