Quint (Robert Shaw) keeps an M1 Garand aboard his boat and is seen using it during the shark's night attack. Chief Martin Brody (Roy Scheider) uses the Garand against the shark at the climax of the film. Several Coast Guardsmen are also armed with M1s, most notably when they surround the two boys wearing a fake shark fin.
As is customary for "hero" weapons, the production rented at least two M1 Garands from Stembridge Gun Rentals which served as the rifle designated for use by Roy Scheider and Robert Shaw, which were later inherited by Cinema Weaponry after their acquisition of the Stembridge Title I firearm inventory. One of the M1s used in the film was sold by Heritage Auction in 2018. The other remains under Cinema Weaponry ownership and has been loaned to the NRA museum in Fairfax, VA for display.
M1 Carbine
One of the men patrolling the waters on the Fourth of July is armed with an M1 Carbine. The rifle, which is often without a magazine loaded, appears to be fitted with adjustable rear sights as seen on post-WW2 M1 Carbines, but without the bayonet lug.
Carcano Rifle
When posing with what they believe to be the shark causing all the carnage, one of the men in the group (at the far right) carries what appears to be an Carcano M91/41. Not implausible; the movie was filmed in 1974 and war souvenir firearms were still very plentiful and affordable.
Remington 700
A Remington 700 is seen in the hands of another shark hunter posing with the shark. In a deleted scene, this person is seen holding the rifle as he fights with other hunters on the waters.
Winchester Model 1892
Winchester Model 1892 rifles are seen in the hands of some shark hunters as well as some of Brody's deputies.
Winchester Model 61
Another shark hunter is seen with what appears to be a a Winchester Model 62 .22 LR pump action rifle
Handguns
Smith & Wesson Model 15
Chief Brody (Roy Scheider) uses a Smith & Wesson Model 15 revolver as his issued sidearm and uses it to fire several shots at the shark as it passes the Orca.
Shotguns
12 Gauge Double Barreled Shotgun
During the chaotic point in the movie, when the fishermen descend on the town in search of the reward on the shark, one of the hunters carries what looks like a Stevens 311A 12 Gauge Double Barreled Shotgun. This is from a deleted scene that can be viewed in the 30th Anniversary Edition's extras features.
Ithaca 37 Field Gun
What appears to be a field variant of the Ithaca 37 is used by another shark hunter in a deleted scene.
Other
Greener Light Harpoon Gun
The harpoon gun used by Quint (Robert Shaw) is a Greener Light Harpoon Gun with a nickel finish. He stores the rifle in its original take-down case, and the line holder has been removed from the forend and the reel is instead attached to the ship to handle bigger fish like sharks.