"When combined with a weapon, an unlimited number of bullets become available."
The Inf. Bullets is a unique item in Resident Evil 3: Nemesis. Combining it with a weapon gives it infinite ammo. It appears as a case full of ammunition.
The item can only be obtained when playing the game for the second time or more on Hard Mode. Players will only have the opportunity to get the item during the seventh encounter with Nemesis, which will be in the Clock tower after playing as Carlos and giving the Anti-Virus vaccine to Jill Valentine whilst having defeated it in every other encounter up to that point. Nemesis will drop the Inf. Bullets when the player defeats him in his second form (it would normally drop the M4A1 rifle if the player was on their first play-through).
Infinite Bullets can be combined with any single weapon. After combining, the case will disappear and the weapon will gain infinite ammunition. Players will have the option to switch between regular handgun ammo and enhanced handgun ammo when using the Hand Gun, and between standard shotgun shells and enhanced shells when using the Shotgun. Also, it's possible to switch between any kind of rounds when using the G. Launcher.
Loading the Mine Thrower with infinite bullets will change the effect of rounds it fires; darts will turn into home onto targets, which seek the enemy and blast through anything on its way. Infinite ammo indicator will be red and the effect of rounds can not be changed to the original.
Another way to acquire infinite bullets is to buy it for $9999 in The Mercenaries - Operation: Mad Jackal, but all the weapons will be loaded with infinite ammo and you can not undo this effect.