The following weapons were used in the film Undoing:
The two thugs that attack and rob Samuel (Sung Kang) and Joon (Leonardo Nam) at the beginning are armed with Beretta 92FS pistols.
Beretta 92F - 9x19mm. The cosmetic differences are very slight and hard to see. Most of the changes are the inner workings of the gun.
A thug holds his Beretta on Joon
Samuel holding a Beretta dropped by one of the assailants
Smith & Wesson Model 60
At one point in the film Randall (José Zúñiga) takes a Smith & Wesson Model 60 from his safe and apparently contemplates suicide.
Smith & Wesson Model 60 - .38 Special / .357 magnum
Crime boss Danny (Kenneth Choi) shows of a Glock 17 he recently acquired to Randall whom he is extorting money from, going so far as to hand him the weapon, subtly taunting him to take revenge. He states that he recently purchased the weapon for $3200, about five times MSRP for a new Third generation Glock 17.
A Generation 3 Glock 17 9x19mm. Note the finger grooves, thumb reliefs, and accessory rail on the frame, which differentiate it from the older model.
Danny brandishes his new Glock
Danny hands the weapon to Randall
Samuel (Sung Kang) retrieves a 1911 from a box in his car's trunk to use in his shootout at the end with Leon (Russell Wong). Don (Tom Bower) takes the weapon from Samuel to hold Leon at gunpoint allowing Samuel to escape.
Pre-War Colt M1911A1 Pistol Commercial - .45 ACP
Samuel takes out his 1911
Samuel takes cover behind a car
Samuel corners Leon with his 1911
Samuel holds his gun on Leon
Don takes the 1911 from Samuel, allowing Samuel to escape
Leon carries a Beretta Inox during is fight with Samuel.
Beretta 92FS INOX - 9x19mm.
Leon's Beretta Inox is knocked to the ground
Leon picks up his Beretta
A deleted scene I forgot to screen cap gives a much clearer picture of this weapon.