Resident Evil 0

This isn't much of an answer, but I don't believe the game say the actual name of the gun Billy uses. I think it says something like "Army issued" or something.

The game calls Billys gun a Handgun, and no name or model number is given. The in-game description for Billys handgun says "A standard army issued handgun". My belief is that the gun is probably modeled after the type you mentioned, but the number of rounds it holds was changed for gameplay reasons. Ranting and raving: Why is it an ARMY gun, when Billy is an ex-MARINE? Why would the army be taking Billy to his execution? I would think he would be escorted by Marine Corps or Navy MPs, but I know nothing about the military, so thats as I good as I can guess.

Id guess that it was a berretta M9, since its been the standard issue handgun since '90 or something, an issued 1911 would probably be a little more simplistic, not to mention use .45 ammo, while its stated a thousand times that billy/becca's guns use 9mm, wich would explain why it holds more.

I don't know, but whatever it is, it has a slightly higher chance of inflicting critical headshots on zombies when compared to Rebecca's handgun.

Its a berretta M9