Resident Evil 0

pretty easy to do this

1. beat the game on easy. shouldnt be that challenging.

2. obtain rank A on leech hunter mode. this will unlock infinite ammo for:
-handgun
-shotgun
-grenade launcher
-hunting gun
-magnum
probably other guns too, but those arent necessary

3. replay the campaign, first using the pistol, until the hunting gun is found
(in the upper floor of one of the train cars before the first boss battle)

use that until you reach the shotgun in the mansion.
(found in one of the dark rooms with a ladder that leads to a long walkway/balcony outside, and a door that leads to the hallway where the steamroom is located)
i usually give this to rebecca, and use her to clear out the art room on the upper right side of the mansion (from the main doorways perspective) here is where youll find the grenade launcher, which i give to billy.

use the combo of those 2 for the rest of the game, and once you come across the magnum in the tramway cart, use that for billy and youre set.

if youre really careful, you can get both this and the achievement for not healing in one easy go. took me roughly 2 and a half hours to get

hope this helps

*edit* thank you Gaming Bear 33 for bringing it up

If you get rank A on leech hunter you can find a magnum revolver with infinite ammo on the train. It is located on a bed in the cabin (with a dead body) next to the first save room onboard the train (room 202) This weapon will one shot most enemies and it only takes up one item space.

i am uncertain if this gun can be found on easy, but it is possible to do this on normal or hard for sure. Also if doing this on the harder difficulties, might as well try and get an S rank with the infinite ammo everything right?

Its recommended that you first beat the game on S Rank (beat game in under 3.5hrs) and get the unlimited launcher. Or alternatively get the infinite ammo guns by playing Leech Hunter. With the unlimited guns it will make this run a lot more easier as you can take your time and destroy everything, even bosses, in one hit. Dont let your guard down you can still die even with being almost god like. My first attempt in the battle arena the hunters kept slashing me and having me stun locked until i died and forcing me to re-do everything. Also while doing this run though without saving, with the unlimited rockets at your side you shouldn't need to heal at all thus also netting you the achievements for not healing, combining herbs, etc. Just take it slow and easy and youll get this in no time

U can Unlock This Achievement Pretty easy. I Unlock this Achievement In Wesker Mode with Infinite Ammo. Plus I used the Magnum Revolver u get in the Train for beating Leach Hunter with collecting 100 Leaches. Here is a Full Walkthrough Video how I beat Wesker Mode without Saving the Game. U will Unlock this Achievement once u beat the game. Hope this helps :)

Si no quieres complicarte en obtener este logro te recomiendo terminar el juego un par de veces para saber que hacer en cada momento y completar el minijuego leech hunter con rango A para obtener armas con munición infinita, con esto hecho inicia una partida extra en dificultad fácil y pan comido.
Si buscas un reto te invito a iniciar una nueva partida en dificultad normal o en difícil, si optas por esto debes gestionar bien tus recursos sobre todo en difícil, en lugar de pelear evita a los enemigos, solo acaba con ellos cuando sea necesario, planea bien la ruta para no dar tantas vueltas, utiliza al personaje indicado para cada situación, Billy es mejor en combate y mas resistente por lo que querrás usarlo la mayor parte del tiempo.
Te dejo un video de mi recorrido en modo normal sin guardar y sin utilizar munición infinita, buena suerte!