After initially being seen handling the distinctive wooden holster/stock, Bubba Zanetti (Geoff Parry) briefly attempts to use a Mauser C96 pistol to shoot a mannequin when the other bikers are messing around at the beach. He begins to aim, but stops when Johnny runs out in front of him with Toecutter's shotgun.
Smith & Wesson Model 28
The MFP carry Smith & Wesson Model 28 as their standard issue. Although they are rarely drawn and seen mostly in their holsters. Bubba is seen firing one at Max near the end of the film. When Max puts on the "Grumpy" mask when his wife is mad that he is going in to work early because Goose wants him to, their baby is seen on the living room floor, apparently playing with Max's revolver.
Smith & Wesson Model 13
Jim Goose appears to carry a 3" Smith & Wesson Model 13 when he and Max inspect the aftermath of the attacked couple.
Double Barrel Shotguns
A Bentley shotgun of the same model listed below as the sawn-off, quite possibly the same shotgun later cut down for Max's use. Notable are the same white ring around the base of the grip, the proportions of the steel receiver (namely the flat space between the end of the chamber and the back of the receiver), and the same checkering pattern and locking screw on the forearm.
First seen in the hands of eager MFP patrolman Roop (Steve Millichamp) when he tries to shoot the Night Rider in the film's opening. Another is used by Johnny (Tim Burns) to shoot a mannequin when the bikers are at the beach. Max also keeps one of these weapons close by after he resigns from MFP and goes traveling with his wife and child.
Late in the movie, "Aunt May" Swaisey (Sheila Florance), the old woman that Max and family are staying with, uses a very old, exposed-hammer shotgun to herd Toecutter's biker thugs into a shed.
Could be a Charles Parker 1878 side by side.
Sawed-off double-barrel shotgun
Max (Mel Gibson) carries as his main weapon possibly a Savage/Stevens 311A Shotgun, but more likely a VG Bentley for the same reasons as above. Possibly the same weapon Roop carries, looking at the bluing patterns on the receiver and noting the extreme budget limits of the film. When battling against the Biker Gang, Max for some odd reason makes an effort to reach this shotgun when his leg is damaged but is armed with a S&W 28 and doesn't even use it when he can.
Winchester Model 1912
Max carries a Winchester Model 1912 when he and Jim Goose inspect the aftermath of the attacked couple. It appears to be a long barreled sporting version.