The Handgun is Billy's starting weapon in Resident Evil 0. It is never explained how Billy retrieved the gun in-game, presumably from the Military Police officers that transported him after they were killed by Cerberus, but in the novelization, Billy finds it amongst the cargo in the Ecliptic Express and it is mentioned how the army was issued with an identical pistol.
The Handgun will be part of Billy's inventory when he joined Rebecca in the game. It is slightly more powerful and has a higher critical headshot rate than Rebecca's Samurai Edge Handgun, as well as having a louder gunshot when fired. It is highly accurate and is perhaps more useful over Rebecca's 'Samurai Edge'.
The Handgun Parts can be collected and added to the handgun to increase further its chance of a decapitation attack, as well increase the rate of fire.
Billy also starts with his Handgun in Leech Hunter in his inventory and an already Custom Handgun can be found in during both item patterns. It is on the bed of the Infirmary and will only have 8 bullets in it.
- Examine: Handgun
"A standard army-issue handgun. It uses 9mm parabellum rounds."
- Examine: Custom Handgun
"A custom handgun that's been fitted with a scope for greater accuracy. These modifications should make it easier to hit a target's weak point."