Before the 2004 film version of The Punisher starring Thomas Jane, there was this 1989 "B movie" starring Dolph Lundgren, as the protagonist Frank Castle.
In the Casino scene, Frank Castle uses an M60, with a long barreled 37mm grenade launcher mounted underneath(!!!). Talk about making your primary weapon as heavy as possible!. It's not an M203, but some mocked up launcher (see photos).
Regarding the launcher, Its probably a S&W 37mm riot gun or some flare/naval rope launcher, Something like that was used in the Chuck Norris movie Invasion USA to take place of the M203 on M16 rifles.
Frank Castle fires this shotgun at the docks. Amazing how a 7 shot tube can fire 18 shots without reloading.....
Acetylene "non" gun
Common in movies where they could not use real guns (like in places with noise restrictions, around small children, or close to an actor's head). Also New York City also has draconian anti gun laws, thus these FAKE guns which fire a 'poof' of acetylene flash and smoke are used instead of real blank firing guns in many instances. (Most noticeable in the movie the Siege when used by Denzel Washington). These fake guns look a little similar to major models of handguns (Beretta 92, Glock, M1911) but something about them always looks a little 'off'.
Sawn-off double barrel Shotgun
Used by Castle during the raid on the Yakuza stronghold.
Thompson 1928 Sub-Machinegun
Used by Castle when he is breaking all the kids out of the jail, he however loses it and never uses it
Colt Commando
Frank Castle is seen using a Colt Commando with a small silencer screwed on the muzzle while he was raiding the Yakuza stronghold towards the end of the film.