What appears to be a Glock 19 is used by Betty Cooper (Lili Reinhart) in "Chapter Eighty-One: The Homecoming" while on sabbatical from the FBI Academy, which she laters use as her personal sidearm.
Makarov PM
A suppressed Makarov PM is used in "Chapter Seventy-Eight: The Preppy Murders" by Hermosa Lodge (Mishel Prada). Hiram Lodge (Mark Consuelos) uses it at the end of "Chapter Eighty-Eight: Citizen Lodge".
M1911A1
An M1911A1 is used by Hiram in Archie's dream sequence in "Chapter Eighty: Purgatorio". A stainless type appears to be seen in "Chapter Eighty-Six: The Pincushion Man" and in "Chapter Ninety-Three: Dance of Death".
Taurus PT92
A stainless Taurus PT92 is seen with disgraced FBI agent Charles Smith (Wyatt Nash) in "Chapter Eighty-Six: The Pincushion Man". It's later seen in other episodes, usually as a one-off pistol.
Unknown
Revolvers
Colt Python
A Colt Python is used by Jeremiah Petersen (Jonathan Bryant) in "Chapter Eighty-Seven: Strange Bedfellows".
Rossi Model 971
A Rossi Model 971 is used by Betty as her personal sidearm. Alice Cooper uses it at the end of "Chapter Ninety-Five: RIVERDALE: RIP(?)".
Smith & Wesson Model 29
What appears to be a Smith & Wesson Model 29 is seen on the cover of Jughead's debut novel The Outcasts.
Smith & Wesson Model 36
A Smith & Wesson Model 36 with stainless grips in a stainless finish is seemingly used by Chad after Hiram Lodge gives it to him to assassinate Archie in "Chapter Ninety-Three: Dance of Death". Hiram says that he obtained it as a ghost gun. It also appears to be used by Veronica in "Chapter Ninety-Five: RIVERDALE: RIP(?)".
Unknown
Shotguns
Benelli M4
Benelli M4s are used by Hiram's men in "Chapter Eighty-Three: Fire in the Sky".
Ithaca 37
An Ithaca 37 with a short barrel is held by an armed man accosting Veronica outside Pop's in "Chapter Seventy-Eight: The Preppy Murders". The riot version is used by Reggie Mantle (Charles Melton) while working under Hiram Lodge, first seen in "Chapter Eighty-Three: Fire in the Sky".
A Remington 870 Slug Gun appears to be seen at the end of "Chapter Ninety-Five: RIVERDALE: RIP(?)" with Sheriff Keller.
Sawed off shotgun
A sawed off 12 Gauge Double Barreled Shotgun is seen with Reggie at the end of "Chapter Ninety-Five: RIVERDALE: RIP(?)". It's never fired.
Assault Rifles
AMD-65
The AMD-65 is used by a Vito mob soldier in a drive-by in "Chapter Eighty-Eight: Citizen Lodge".
Battle Rifles
M1 Carbine
The M1 Carbine is seen in Archie's (KJ Apa) dream sequence in "Chapter Eighty: Purgatorio", used by Riverdale High students in WWII combat uniforms and gear.
M1 Garand
The M1 Garand is also used by Riverdale High students during Archie's dream sequence in "Chapter Eighty: Purgatorio". They're later seen with soldiers seen in Archie's various hallucinations.
Bolt-Action Rifles
Unknown
Others
Bow
A bow is used by Cheryl Blossom (Madelaine Petsch) in "Chapter Ninety-Five: RIVERDALE: RIP(?)" when she uses it to persuade Hiram to leave Riverdale.