A Beretta 92FS was used by Eli Matchett (Don Harvey) throughout "Eli Matchett (No. 72)". Ex-CIA asset and Cabal agent Matias Solomon (Edi Gathegi) uses one near the end of "The Director (No. 24)" to threaten Special Agent Ressler.
A Beretta Px4 Storm Compact was Liz's backup sidearm, seen in "Mr. Gregory Devry (No. 95)" when her FBI credentials were revoked.
Colt M1911A1
A Colt M1911A1 is seen with Baz (Bazzel Baz) when he detains Zal Bin Hasaan aka Shahin Navabi near the end of "Zal Bin Hasaan (No. 31)", being used as his main sidearm. Reddington used one back in his time in Paris near the end of "Alistair Pitt (No. 103)".
The Glock 17 was briefly seen with Reddington when he disguises himself as a Metropolitan Police Department of the District of Columbia (MPDDC) officer at the start of "The Troll Farmer (No. 38)". Dembe briefly uses this in a shootout near the end of "Arioch Cain (No. 50)". Cabal agents use them as their sidearm with Tom using one in "Kings of the Highway (No. 108)" to take down Cabal assassins with Laurel Hitchen (Christine Lahti) and Jilly (Danielle Burgess) using one in the same episode. A silenced Glock 17 is used by an assassin at the start of "Mr. Gregory Devry" (No. 95). Noah (Mark Blum) uses it briefly in "Lady Ambrosia (No. 77)".
Glock 19
The Glock 19 is seen in the hands of Special Agent Donald Ressler and a few FBI agents throughout the season as their main sidearm. Matias uses one with a suppressor and taclight module as his main sidearm. A Glock 19 is used by Zal Bin Hasaan (Sammy Sheik) after he takes it from a disarmed Mossad kidon officer in the middle of "Zal Bin Hasaan (No. 31)". Aram uses the Glock 19 to stall Keen's "transfer" from the Post Office near the end of "The Director (No. 24)". Rafael Vaccaro (Giorgio Panetta) uses one at the start of "Alistair Pitt (No. 103)". Matias now uses it as his sidearm after being bailed out of US Marshals custody, first seen in "Mr. Solomon: Conclusion". Baz appears to use it near the end of "Susan Hargrave (No. 18)".
Glock 26
A Glock 26 is seen with Tom Keen as his backup sidearm in the season.
IWI Jericho 941 Compact
An IWI Jericho 941 Compact is used by a gunman in "Cape May".
Kimber Custom TLE II
A Kimber Custom TLE II is used by Reddington briefly in "Cape May" when he takes it from a dead gunman.
Makarov PM
A Makarov PM is seen with a FSB agent/Russian Consulate employee in "Marvin Gerard (No. 82)" before Liz takes it while on the run.
SIG-Sauer P229R
The SIG-Sauer P229R is used multiple times throughout Season 3.
A Smith & Wesson 5906 is seen used by a 18th Street Gang member when he takes Agent Navabi (Mozhan Marnò) hostage in the middle of "The Troll Farmer (No. 38)" (S3E01).
A Smith & Wesson M&P Shield is now used by Elizabeth Keen instead of a Glock 19 in the season ever since she was publicly branded a double agent for the FSB. Gina Zanetakos (Margarita Levieva) uses it with a suppressor as her main sidearm. Samar is seen with it in "Mr. Solomon (No. 32)". It's used by Artax Network agent Nez Rowan (Tawny Cypress) in "The Artax Network (No. 40)".
Walther PPK
A Walther PPK is seen with Gregory Devry (Jake Weber) in the middle of "Mr. Gregory Devry (No. 95)".
Revolver
Smith & Wesson Model 19 Snub Nose
A Smith & Wesson Model 19 Snub Nose is seen used by Harold Cooper (Harry Lennix) at the start of "Kings of the Highway (No. 108)" to shoot a Cabal assassin by surprise, later using it as his personal sidearm.
Smith & Wesson Model 36
A Smith & Wesson Model 36 was used briefly by a plainclothes officer (Scott Johnsen) near the end of "Eli Matchett (No. 72)".
Submachine Guns
CZ Scorpion Evo 3 S1
CZ Scorpion Evo 3 S1 submachine guns are used by most of the mercenaries recruited to work with Solomon in "Mr. Solomon (No. 32)" with Reddington using it after disarming one of them.
KRISS Vector
Some of the mercenaries recruited to work with Solomon use KRISS Vectors equipped with EOTech sights in "Mr. Solomon (No. 32)".
SIG-Sauer MPX-P
Some of the mercenaries recruited to work with Solomon use SIG-Sauer MPX-Ps in "Mr. Solomon (No. 32)" as their main weapon.
Assault Rifles
AKS-47
AKS-47s appear in the hands of SVR Zaslon Spetsnaz commandos in "Marvin Gerard (No. 82)".
AKMS
The AKMS is widely seen in the season with various characters.
AKMSU
AKMSUs are seen with Russian civilian/paramilitary personnel and by criminals in the season.
Colt LE Carbine
The Colt LE Carbine takes the place for M4A1-type assault rifle used by American and Dutch law enforcement and Cabal agent in the season. One of Reddington's mercenaries is seen with the LE Carbine in "The Director (No. 24)". Mr. Fox handles one in the middle of "Alistair Pitt (No. 103)". Baz, Dembe and Reddington's other mercenaries use them throughout "Mr. Solomon (No. 32)", serving as their main assault rifle.
Colt M4A1
A Colt M4A1 is seen with Verdiant employee Gabriel Costa (Gabriel Sloyer) at the start of "Eli Matchett (No. 72)". One FBI SWAT officer is seen with it near the end of "The Djinn (No. 43)".
Colt Model 933
The Colt Model 933 is used by various American law enforcement personnel. One is used by an armed kidnapper near the end of "Mr. Gregory Devry (No. 95)".
Czech Small Arms SA vz. 58 Compact
Czech Small Arms SA vz. 58 Compact assault carbines are used by some of the mercenaries recruited to work with Solomon in "Mr. Solomon (No. 32)".
Heckler & Koch G36C
Heckler & Koch G36Cs are used by some Cabal agents equipped with ACOG scopes as their main weapon in the season. Ressler and Karakurt use them from deceased Cabal agents in "The Director (No. 24)".
Mk. 18 Mod 0
Mk. 18 Mod 0s are seen with Dembe and Baz in a raid at the end of "Susan Hargrave (No. 18)".
SIG P556 SWAT / SG 550 hybrid
SIG P556 SWAT assault rifles are used by some Cabal agents as their main weapon in the season.
SIG-Sauer 516
At least one SIG-Sauer 516 assault rifle is seen in "The Director (No. 24)".
A Mossberg 500 Cruiser shotgun was briefly used by Reddington in the middle of "Marvin Gerard (No. 82)" when he disable a marked MPDDC squad car, using it as his main shotgun of choice. Rafael Vacarro uses one in a shootout near the end of "Alistair Pitt (No. 103)".
Remington 870 Slug Gun
A Remington 870 Slug Gun with black synthetic furniture is used by an armed gunman in "Cape May".
Rifles
Winchester Model 1866 "Yellow Boy"
A Winchester Model 1866 "Yellow Boy" is seen in the cabin, which Tom uses to take out Cabal agents near the end of "The Director (No. 24)".
Bolt-Action Rifles
CZ 550 Magnum
A CZ 550 Magnum was briefly used by Reddington in "Arioch Cain" when he intimidates an underground gun maker to provide info about an assassin called Wendigo in the middle of "Arioch Cain (No. 50)". During the episode, he comments that he fired one in Africa chambered in .416 Rigby.
Sniper Rifles
Barrett M82A1M
A Barrett M82A1M fitted with a scope with a BORS ballistic computer is used by a mercenary sniper in shooting Reddington's convoy at the end of "Mr. Solomon: Conclusion".
Unknown
Grenades
Smoke Grenade
A smoke grenade was used in an assault on a cabin in "The Director (No. 24)".
Others
Underground Armory
A variety of small arms are seen in a underground arms maker in "Arioch Cain (No. 50)".
Reddington Safe House
A few Remington 700PSS sniper rifles are seen in Reddington's West Virginia safe house in "The Director (No. 24)".