Christopher Smith aka Peacemaker (John Cena) carries the same modified stainless Desert Eagle Mark XIX from The Suicide Squad. It appears to be a custom barrel attachment just slipped over the standard 10" barrel, akin to The Boondock Saints II: All Saints Day. Peacemaker is somewhat a parody character and extreme and somewhat comically over the top violence is a common motif, so it would check out that he would be equipped with an absurd handgun so pointlessly large that even a completely gun-illiterate viewer could pick up on the joke.
Beretta 92FS
The Beretta 92FS is carried by uniformed officers of the Evergreen Police Department.
Glock 17
Emilia Harcourt (Jennifer Holland) carries a second generation Glock 17 throughout the season. "In Better Goff Dead", she tells Peacemaker that her first Glock was a Glock 20, a gift from her parents when she was 12 years old. the Glock she uses in the show was most likely a Glock 17, not necessarily the Glock 20 as previously identified. Christopher Smith / Peacemaker (John Cena) disarms an infected Detective Sophie Song (Annie Chang) of her third generation Glock 17 in "It's Cow or Never", which is a continuity error to her Glock 19 as depicted in the first seven episodes.
Glock 19
The Glock 19 is seen used by Detective Sophie Song (Annie Chang) as well as Detective Larry Fitzgibbon (Lochlyn Munro) of the Evergreen Police Department.
Heckler & Koch P30L
Emilia starts carrying a Heckler & Koch P30L as her sidearm in "Stop Dragon My Heart Around" (S1E07) and "It's Cow or Never" (S1E08), having previously carried a Glock 17 for the majority of the season.
Luger P08
The Luger P08 is carried by a Neo-Nazi loyal to August Smith / The White Dragon in "Stop Dragon My Heart Around". It is later used by Christopher in the same episode.
SIG-Sauer P228
Clemson Murn (Chukwudi Iwuji) uses a SIG-Sauer P228 as his personal sidearm. "In Better Goff Dead", Murn gets an additional one out of a crate to hand to Leota Adebayo (Danielle Brooks). Leota is seen using it as her personal weapon until the end of the season.
Walther P99
Adrian Chase / Vigilante (Freddie Stroma) carries a two-tone Walther P99 with a slightly bronzy-tinted stainless steel slide as his personal sidearm, which he keeps in a hip holster when not in use.
The Single Action Army is used by Adrian and Christopher in "Best Friends for Never".
Submachine Guns
FN P90
The FN P90 is carried by the A.R.G.U.S. team as one of their primary small arms, and is used by Adrian Chase / Vigilate (Freddie Stroma), John Economos (Steve Agee) and Christopher Smith / Peacemaker (John Cena).
MasterPiece Arms MPA30DMG
The MasterPiece Arms MPA30DMG is used in "Best Friends for Never" by Adrian. While clearly being the submachine gun variant, it seems that Adrian took the folding stock and the first 4 inches of the handguard off of its larger carbine variant, the MPA300DMG. He also uses it with BCM Mod 3 Vertical grip and a raised reflex sight.
Assault Rifles
Colt Model 715
A Colt Model 715 is carried by officers of the Evergreen Police Department as their rifle of choice. This weapon is friequently seen in films/TV shows shot in British Columbia, Canada, where the show was filmed.
Colt M4A1
The Colt M4A1 is seen in "Stop Dragon My Heart Around" with hooded Neo-Nazis.
Heckler & Koch HK416D
Christopher uses a Heckler & Koch HK416D carbine with a 10.4" barrel in "Best Friends for Never".
Shotguns
Kel-Tec KSG
A Kel-Tec KSG with a white dove on the stock is used by Christopher, first seen in "Best Friends for Never".
Mossberg 500 Cruiser
A Mossberg 500 Cruiser with a stainless finish is used by Adrian in "Best Friends for Never".
Remington Model 870
The Remington Model 870 is seen in "Better Goff Dead" and in "It's Cow or Never".
A Barrett M82A1M with an FDE finish is used in "Better Goff Dead".
Grenades
M67 hand grenade
A M67 hand grenade taped to a Russian-made tank gun shell is used by Christopher to take out several Butterfly-infected humans in "Monkey Dory", which he later does it again at the end of "It's Cow or Never". This is also used by Adrian in "Stop Dragon My Heart Around".
In real life, this is a very common way of making cost-effective IEDs in locations where Russian military surplus is common and cheap.