Most of the usable guns in the game are real life guns under a nickname.

Default "Silver Ghost handgun" = H&K USP/S&W Sigma/Ruger P85 hybrid
Punisher = FN Five-seveN
Red9 = Mauser C96 (Red9 was an actual nickname for Mauser variants that handled 9mm bullets)
Blacktail = Springfield Armory XD
Matilda = Heckler & Koch VP70M (The very same pistol that Leon used in RE2, with its stock attachment and burst fire mode active)

Shotgun = Remington 870
Riot Gun = customised Benelli M3 Super 90
Striker = Armsel Protecta ("Striker" was the gun's original production name)
Ada's Shotgun = Mossberg 500

Rifle = Springfield M19031A1
Semi-auto Rifle = Heckler & Koch SL8

Broken Butterfly = S&W Schofield Model 3/Colt Single Action Army hybrid
Killer 7 = Colt M1911 magnum variant with an AMT Hardballer-style laser sight
Handcannon = Smith & Wesson Model 500

TMP = Steyr TMP. HUNK uses a customised variant resembling the Brugger & Thornet MP-9
Chicago Typewriter = Thompson submachine gun. Leon normally uses the M1A1 Army service variant while Ada and Mobster outfit Leon use the famous 1921 drum magazine version. "Chicago Typewriter" was one of many famous real life nicknames for the Thompson.

Rocket Launcher = RPG-7

The only truly fictional weapons are the Plaga Removal Laser 412, the Mine Thrower and the Bowgun.