The hitman (Mickey Bruno) sent by Carlo Mangano (Leo Rossi) in collusion with Primo Sindone (Chazz Palminteri) to kill Paul Vitti (Robert De Niro) in Miami carries a suppressed SIG-Sauer P230 (Note trigger guard). After Vitti knocks out the hitman, he picks up the pistol himself.
Paul Vitti (Robert De Niro) uses a Beretta Cheetah during Dr. Ben Sobel's (Billy Crystal) mock execution. When Vitti is unable to fire back at the rival mobsters, Sobel himself uses the gun to take out, as Jelly later tells him, a "'72 Chevy and the Amana side-by-side refridgerator". Jelly's (Joe Viterelli) gun becomes a nickel 85F when he fires it at the rival mobsters at the dump.
Taurus PT92
Primo Sidone (Chazz Palminteri) holds what appears to be a Taurus PT92 pistol to threaten Dr. Ben Sobel and later to take a shot at Paul Vitti.
Glock 19
An FBI agent arresting Primo Sidone and his men in the finale carries a Glock 19.
M1911A1
A Mafia hood (Kresimir Novakovic) standing watch outside the Apalachin conference in 1957 pulls out his M1911A1 and threatens a cow that won't move away from his boss's expensive car.
Revolvers
Colt King Cobra
One of the hitmen in Sobel's dream carries a Colt King Cobra revolver.
Smith & Wesson Model 29
During the opening narration by Paul Vitti (Robert De Niro) about the Appalachian raid, he says his father (Bart Tangredi) used a ".44 cannon" (most likely a Smith & Wesson Model 29) to hijack a tractor from an upstate New York farmer.
Smith & Wesson Model 686
Vitti's henchman Jimmy Boots (Richard Castellano) shows off what appears to be a Smith & Wesson Model 686 to intimidate Sobel and later uses it during the shootout at the dump.
The FBI agents and New York state police officers carry Thompson M1s during the opening sequence depicting the 1957 raid of the Mafia's meeting in Appalachian.
Rifles
Winchester Model 1894
An FBI agent leading the 1957 Appalachian raid carries a Winchester Model 1894 rifle.
AKM variants
The two hitmen sent by Primo to kill Vitti at the garbage dump carry several AKM variants.
AR-15/M16 variants
Several mobsters, including one guarding the door and one hired by Vitti, carry M16 variants at the meeting.
Shotguns
Ithaca 37
Mo-Mo (Alfred Sauchelli Jr.) pulls out an Ithaca 37 with an extended magazine tube and rifle sights to intimidate Primo.
Machine Guns
M60
Eddie "Cokes" (Frank Aquilino) and his assistant carry an M60 machine gun and extra ammunition, which Sobel later comments to Vitti on.