Sterling Archer's primary sidearm is a Walther PPK. In the early episodes, the pistol lacked detail, but by the end of season 2, there was so much detail, the serial number was visible. In season 2's "Tragical History" Archer correctly describes the pistol as having a seven shot capacity. According to the companion book How to Archer: The Ultimate Guide to Espionage and Style and Women and Also Cocktails Ever Written, his PPK is chambered in .32 ACP.
Mauser M712 Schnellfeuer
Manfred has a Mauser M712 Schnellfeuer as his sidearm, using it to shoot Torvald Utne (not the Olympic shot-putter) in "Killing Utne."
Beretta 92F
Captain Lammers uses a Beretta 92F in "Skytanic." Archer also uses a suppressed Beretta 92F in one scene in "Skorpio." Lana Kane also carries a pair of Beretta 92F pistols in a dual-pistol shoulder rig.
Smith & Wesson Model 629
Since retiring from the field, Malory Archer's primary handgun is a Smith & Wesson Model 629, tricked out with a scope and laser. She sleeps with it by her beside in "Dial M for Mother."
Desert Eagle Mark VII
Archer's rival, Barry Dillon, carries a nickel Desert Eagle Mark VII which he talks TO, not WITH. Lana Kane also uses a nickel Desert Eagle on occasion.
Luger P08
Krenshaw/Kremensky uses a Luger P08 in the pilot, "Mole Hunt."
Colt Python
Malory uses one in one of her flashbacks in "Job Offer."
Colt Official Police
Sterling is shown with a Colt Official Police in a flashback during "Killing Utne."
SIG-Sauer P226
A SIG-Sauer P226 is seen on the floor in "Skorpio." It is missing most of its controls.
Unidentified pistol
Major Jakov's assistant uses an unknown pistol in "Dial M for Mother" (S01E10).
Submachine Guns
TEC-9
Lana Kane is often seen with a pair of TEC-9's, which would be a good fit for her Johnny Bench-ian, steam-shovelly, Truckasaurus hands. According to the dialogue, they are TEC-9s, and fire full auto, but lack the sling rings of a TEC-9.
MP40
The MP40 is the SMG seen most on "Archer." ODIN agents use it almost exclusively, as do gay interior decorators/assassins for hire Charles and Rudy in "Hon
Steyr TMP
Some members of a Cuban hit squad are armed with Steyr TMP SMGs ("Diversity Hire.")
Uzi
Other members of the Cuban hit squad are armed with Uzi SMGs ("Diversity Hire.")
Rifles
AK-47
The AK-47 shows up numerous times during the series. They appear to be based on real AK-47s, with the milled receiver and open-topped front sight.
M14
Cyril channels Private Pyle from Full Metal Jacket with an M14 after Lana decides to sleep with all the men at ISIS as a form of revenge in "Dial M for Mother."
M21
An M21 rifle is seen in a crate during a flashback to the last moments of Agents Ruiz, Pak, and Mgumbe (all of which recycle the same background) in "Diversity Hire."
Heckler & Koch PSG-1
Except in one instance, the Heckler & Koch PSG-1 is the primary sniper rifle of ISIS.
Ramon Limon has a M18A1 Claymore handy to decorate Malory's old apartment in Miami ("Honeypot"). Archer, showing some competence, disarms a Claymore in "El Contador".
M67 hand grenade
Archer pulls out an M67 hand grenade after Skorpio confronts Lana and him after their threesome.
Miscellaneous
Rocket Launcher
Skorpio's henchmen prepare to fire rocket launchers at Archer and Lana in "Skorpio." These are probably supposed to be FIM-43 Redeye missiles, since Skorpio was supposed to be selling them, but don't look like Redeyes at all.
".25 cal Chekhov"
This is the pistol that Archer gives to Cyril in "Training Day." The name comes from the literary technique "Chekhov's gun," which comes into play later in this episode. It's never seen again after "Training Day." Possibly a North American Arms Guardian chambered in .25.
Scaling issues
Scaling, as seen in the armory shots above, used to be a problem, especially in the early episodes.