Donald walks into an N.Y.P.D. building brandishing a Smith & Wesson Model 38 revolver. The response is he is put into a choke hold and finds dozens of handguns pointed at him.
When Donald comes out of the cabin, he uses a M1911A1 clone that has an external extractor, thus strongly indicating that it is a Spanish STAR Model P, impersonating a Colt M1911A1 pistol.
Browning Hi-Power
Having had his M1911A1 taken by police, Jack Locke (Jerry Reed) appears again to torment Sonny Paluso (Walter Matthau), this time holding a Browning Hi-Power Pistol with the "Beer Can" Adjustable rear Sights.
Smith & Wesson Model 29
While shopping at the Gun Store, Donald Quinelle asks to see a .44 magnum revolver, whereas, the clerk hands him a Smith & Wesson Model 29 with 8 3/8th " Barrel.
Among the many firearms that Donald looks at while shopping at the all night gun-store is what appears to be a nickel plated Cobra Derringer. The model was brought out originally by the Davis firearms company in 1982 so it fits into the time frame of the movie b production date. When Davis went bankrupt in 1998 the company's product line was purchased by Cobra and production continues to this date (2021).
Ruger Super BlackHawk
When Donald Quinelle (Robin Williams) visits the gun store, he beholds an Armed Little Lady (Norma Pratt) who asks for and receives a Ruger Super Blackhawk revolver chambered in .44 magnum.
Nickel Single Action Army
In an absurdist scene, Sonny Paluso (Walter Matthau) tries to have a heart to heart talk with his 16 yr old daughter, (Kristen Vigard), but a porno is playing on the VCR in the background. In the 'porn' real life porn stars are acting in a feature called "How the West was Wet". Porn star Marc Stevens is seen pointing a nickel Single Action Revolver towards real life porn actress Tiffany Clark where she proceeds to do 'oral things' to it before they have sex.
Shotguns
Winchester Model 1897
One of the Survivalist students carries a Winchester Model 1897 (non-Takedown Model) shotgun during training - 12 gauge.
During snow survival training, Donald Quinelle (Robin Williams) uses a full auto Uzi Submachine gun, which, by the way is not a weapon one can buy over the counter from a gun store, even in 1983. This same weapon, however, is seen hanging over the fireplace in Donald's personal cabin which strongly implies that it is his and not a loaner.
Smith & Wesson 76 Model Submachine gun
Several of the survival training students are seen with full automatic firing Smith & Wesson Model 76 submachine guns. At this time, Smith & Wesson were still selling the semi-auto only 16" barrel carbine of the same weapon over the counter. It is assumed (in the context of the story) that these were semiautomatic carbines that were later chopped and converted by their owners.
MAC-10
One of the survivalist students appears to be carrying a MAC-10 with a suppressor.
Donald uses an M72 LAW Rocket as well during the events in Vermont.
Misc
Donald's Cabin Armory
The Gun Store
Many Handguns and rifles are seen on display at the gun store, however, the shots are out of focus being that the camera focuses on Donald and not the back walls.