A Smith & Wesson Sigma with a stainless slide is used in "Elongated Journey into Night" by corrupt Central City Mayor Anthony Bellows (Vito D'Ambrosio).
SIG-Sauer P228
The SIG-Sauer P228 is used by Detective Joe West's (Jesse L. Martin) as his sidearm in the Central City Police Department.
Walther P38
The Walther P38 is seen in "Crisis on Earth-X, Part 3" as the main sidearm of Sturmbannführer Quentin Lance (Paul Blackthorne).
Walther P99
A Walther P99 appears to be seen in "Honey, I Shrunk Team Flash" in a flashback sequence when Barry explains that someone may be framed.
Revolvers
Ruger Speed Six
The Ruger Speed Six is used Ramsey Deacon aka Kilgore (Dominic Burgess) in "Mixed Signals".
Submachine Guns
CZ Scorpion Evo 3 A1
The CZ Scorpion Evo 3 A1 appears in "Enter Flashtime" with some mercenaries in a break-in.
FN P90
The FN P90 is seen with a Iron Height Prison corrections officer in "True Colors".
Heckler & Koch MP5Ks are used by Yakuza wakashus in "Girl's Night Out".
Heckler & Koch UMP
The Heckler & Koch UMP is seen with a mercenary in "Enter Flashtime" during a break-in.
MP40
MP40s modernized with picatinny rails are used by Earth-X Schutzstaffel soldiers in "Crisis on Earth-X, Part 3". Iris West (Candice Patton), Felicity Smoak (Emily Bett Rickards), Oliver Queen (Stephen Amell), Sara Lance (Caity Lotz) and Alex Danvers (Chyler Leigh) use them as well after disarming/killing SS soldiers.
Assault Rifles
AK-47
The AK-47 is seen with armed men in "Don't Run". A few mercenaries use them in "Enter Flashtime".
Colt M16A2
A Colt M16A2 is seen with an Iron Heights Prison corrections officer in "The Elongated Knight Rises".
U
Shotguns
Mossberg 500 Cruiser
A Mossberg 500 Cruiser is seen with Detective West in "The Flash Reborn", but is never fired.
UTAS UTS-15
The UTAS UTS-15 is used by a IHP corrections officer as a shotgun in "True Colors".
Machine Guns
Browning M2HB
The Browning M2HB is used by Earth-X SS forces in "Crisis on Earth-X, Part 3".
Browning M3
A Browning M3 with a 200-round "tombstone" drum is used on a truck in "Crisis on Earth-X, Part 3".
Grenades
Mk 2 hand grenade
A Mk 2 hand grenade is used in "Mixed Signals" by a hijacked CCPD EOD robot.
Grenade Launchers
Sage Control Ordnance Deuce
A Sage Control Ordnance Deuce is seen with the CCPD SWAT and with IHP corrections officers as a non-lethal grenade launcher.
Rocket Launchers
M136 AT4
A M136 AT4 is used in "Honey, I Shrunk Team Flash" by Sylbert Rundine/Dwarfstar (Derek Mears).
Others
Boot
The Boot makes a return from the second season, used to capture Metahumans operating in Central City, using the M14 EBR chassis as its body.
Captain Cold's Cold Gun
Captain Cold's cold gun is seen first in "Mixed Signals" in the hands of Caitlin. One is used by Citizen Cold in "Crisis on Earth-X, Part 3".
Laser Rifle
The laser rifle, based on the UTAS UTS-15 with cosmetic attachments to the upper receiver and barrel, returns to the season. It's first seen in "Mixed Signals". Another one, based on the Steyr AUG A3, is first used by Cisco to ambush Breach in "Elongated Journey into Night".
Oneida Eagle Kestrel
The Oneida Eagle Kestrel is used by Oliver in "Crisis on Earth-X, Part 3".