Burt Gummer (Michael Gross) packs a .50 BMG Barrett M82A1 as his new anti-Graboid weapon in the series. He sports it in the pilot episode "Feeding Frenzy" (S1E01) and uses it to take out a box a half mile away that is putting out sub-sonic noise that is driving the albino Graboid insane. He also arms himself with it in "A Little Paranoia Among Friends" (S1E07) to hunt the Graboid in New Mexico. Tyler (Victor Browne) ends up picking the rifle up when Burt is attacked and uses it to slay the Graboid with messy results.
Sporterized Mauser Karabiner 98K
Burt (Michael Gross) can be seen with a Bolt-Action Mauser Karabiner 98k re chambered to 30-06 with a scope in a couple of episodes. He takes aim on the loose Assblaster in "Blast From the Past" (S1E04) but never gets to fire, Mead (Harrison Page) covers the Assblaster with the rifle while Burt tries to reel it after hooking it with bait using Tyler's "skyfishing" idea. Burt also pulls the rifle from his truck in the opening of "Night of the Shriekers" (S1E03) before switching to the HK33.
Springfield 1861 Rifled Musket
Tyler (Victor Browne), Twitchell (Dean Norris), and Juniper, Arizona resident; George Meadows (William O' Leary), and his baseball team use several antique blackpowder muzzleloading Springfield 1861 rifles to kill the final Shrieker horde with volley fire in the episode "Shriek & Destroy" (S1E13).
Assault Rifles
Colt Model 653
Burt (Michael Gross) is armed with a Colt Model 653 in "Shriek & Destroy" and uses it to take out multiple Shriekers. It can also be seen in the episode "Night of the Shriekers" (S1E03) and used by both Burt and Tyler (Victor Browne) to kill Shriekers as they come into the compound.
Type 56
Tyler (Victor Browne) uses a Type 56 with the stock removed in the episode "Shriek & Destroy" (S1E13) to take care of the Shrieker problem in Juniper, Arizona. It may appear to be an AKM given the slanted muzzle but upon closer inspection one can clearly see the hooded front sight and smooth top reciever.
Heckler & Koch HK33A3
Burt (Michael Gross) retrieves his Heckler & Koch HK33A3 from his truck in "Night of the Shriekers" (S1E03) upon hearing the sounds of Shriekers in the valley. He uses it to slay the first one he comes across. This could also be an Heckler & Koch HK93 since Burt only fires it semi-automatic in the episode.
M16A2
In "Night of the Shriekers", several of Dr. Flint's security personnel including the security chief, Karl Hartung (Patrick St. Esprit) can be seen with M16A2s when they come across Burt after he killed the first Shrieker.
M4A1
An officer of Dr. Flint's security team at the Shrieker rescue test site can be seen with an M4A1 when they encounter Burt in the opening of the episode, another can be seen; slung over and officer's back while locking things down due to the thunderstorm in "Night of the Shriekers".
Submachine Guns
Intratec TEC-DC9
Mobster, Kinney (Michael Rooker) threatens the Perfection Valley residents with an Intratec TEC-DC9 and fires it multiple times at them and their vehicles as they go for cover behind them in "Hit & Run" (S1E06).
IMI Uzi
A Uzi without stock can be seen in the hands of Fish & Wildlife agent Bill McClane (Pat Skipper) to kill Shriekers in the episode "Shriek & Destroy" (S1E13).
Handguns
Magnum Research Desert Eagle Mark XIX
Burt (Michael Gross) carries a nickel finished Desert Eagle Mark XIX pistol chambered in .50 Action Express as a backup sidearm throughout the series. He passes it off to Tyler (Victor Browne) in the episode "Shriek & Destroy" who then uses it to kill a few Shriekers attacking the Pioneer Days festival in Arizona. Twitchell (Dean Norris) also pulls this pistol from Burt's holster and aims it at the mobsters in "Hit and Run" but he drops it as soon as they open fire in their direction. Burt also fires it once in the episode "Flora or Fauna?" (S1E05) to hit a fire extinguisher valve so it'll launch their sand anchor over Plantimal's acid spitting roots.
Dan Wesson SuperMag
Burt (Michael Gross) retrieves a Dan Wesson revolver from his truck in the episode "Project 4-12" (S1E08) and arms himself with it to face the new creature in the valley. The exact variant is unknown, it appears best to be a .445 'SuperMag' variant.
Taurus Model 605
Tyler (Victor Browne) retrieves a Taurus Model 605 revolver from a drawer in Chang's Market in the episode "Project 4-12" and fires a few shots at the monster to no avail. He arms himself with it again at the end of the episode to back Burt up. Tyler has this revolver in his jeep's glove compartment in the episode "Flora or Fauna?" and retrieves it to investigate the missing surveyors. In the episode "The Key" (S1E11) both Frank (Nicholas Turturro) and Delores (Vivica A. Fox) can both be seen with a similar revolver and use it to threaten the residents of Perfection.
Ruger P89
Rosalita (Gladys Jimenez) arms herself with a Ruger P89 in the episode "Hit and Run" (S1E06) and fires a couple of rounds at the mobsters' truck tires and harpoon gun to slow them down. Max (Troy Winbush) also pulls out a similar Ruger P89 pistol when he finally lures El Blanco in to show Frank it's real.
M1911A1
In the pilot episode "Feeding Frenzy" (S1E01), Melvin's hired goon (William Cowart) on the dirt bike pulls a M1911A1 style pistol on Burt when he confronts him. In the episode "The Key" the accountant/hitman (Michael Albala) pulls one on Frank after he unknowingly hitches a ride with him before the screen fades black accompanied by the sound of a gunshot.
Shotguns
Winchester Model 1200
A Winchester Model 1200 shotgun with a birds head style pistol grip is seen on Burt's gun wall in several episodes and used by Rosalita (Gladys Jimenez) to kill Shriekers in "Night of the Shriekers" (S1E03). A similar shotgun is used by Frank (Nicholas Turturro) and Delores (Vivica A. Fox) to threaten Tyler and Rosalita in "The Key" (S1E11), probably the same prop.
Winchester Model 1200 Stainless Police
A stainless police variant of the Winchester Model 1200 can be seen in the hands of Sheriff Sam Boggs (Jim Beaver) of the Bixby police department in the episode "Water Hazard" (S1E12). He fires rubber bullets out of the shotgun in an attempt to slow the shrimp creature down before it reaches the reservoir.
Mossberg 500 Cruiser
A Mossberg 500 Cruiser pistol gripped shotgun can be seen on Burt's gun wall in multiple episodes.
SWD/Cobray Street Sweeper
An SWD/Cobray Street Sweeper can be seen on Burt's gun wall in multiple episodes. Unfortunately we never get to see it in action on a herd of Shriekers.
Blunderbuss
Burt (Michael Gross) uses an antique Blunderbuss to kill the last remaining Shrieker in the episode "Shriek & Destroy" when nothing else is available.