This guide is designed for getting this achievement only. I recommend that this achievement and the one for Claire hardcore are your last two achievements. If they are, you will have the infinite handgun and infinite knife. You will also have a deep understanding of the game mechanics and map layout, and you will need it.
You need to know where zombies are, what windows they will break through, licker spawns, item locations, boss fight points, etc. I used a combination of guides from gamewith.net, VG247.com, IGN.com, and this website. I recommend you use one of those, or notes you make yourself from another playthrough. I'm only providing tips.
First of all, this mode uses ribbons so you need to break the game down into sections and save smart. Sections are
1.RPD
2.Parking Garage
3.Return to RPD
4.MrX to Sewers
5.Sewers
6.Nest
This is a basic example of how to break the game up. Most of the guides I used did this.
*This guide assumes you play scenario A. It’s possible on B but I found A less stressful.
You have (approximately) 27 ribbons. Try to play as though you only have 20. That allows 3 saves per section, 4 if you struggle in a particular area. This allows you to have at least 6 (hopefully more) remaining by Nest and that will allow you to save before AND after the most aggravating parts of the game. I saved 21 times and had 6 ribbons left. I am pretty sure that I found them all.
Now I will list tips somewhat randomly. Hope they help you.
1. Go ahead and accept that most sections will take a second attempt. This will make it less frustrating to reload a save.
2. If you take damage from a zombie, RELOAD. I know this seems frustrating, but I found enough supplies to fully heal around 15 times. You want to save these for bosses, lickers, Mr X, or accidental damage taken at the end of a stressful run. If you haven't went far or gotten much done, reload and try again.
3. Going off tip 2, last resort weapons can help. Have the infinite knife equipped when you know you can get it back, another knife equipped when you can't (plants, Mr X), NEVER use grenades on zombies.
4. Save your grenades for the sewers. The G monsters were almost impossible for me to sneak past on hardcore, and to kill them takes a lot of shotgun ammo. I used 3 grenades as last resort on the 3 G buttholes protecting the king and queen to get past, I did the same on the first one in the walkway, then shotguned the other one in the walkway.
5. Save flash grenades for lickers. Makes them easier to kill. You need to kill the one outside of stars room, the basement of parking garage, and the two in the Nest lounge. You can sneak by the rest.
(West storage & outside of West office)
6. Get all hip pouches! There is one less in hardcore mode than on standard.
7. Ignore the VHS tapes and all of the film with the exception of the hidden location film. It reveals location of fuel & magnum part.
8. Get both spare keys from the portable safes and clear out the safety deposit room.
9. Use the stars badge to get magnum, then again to get the upgrade.
10. Try to clear every room. The room will turn blue when you have everything. Pick up pistol ammo then discard it.
11. Use your infinite ammo pistol to kill ALL zombies. This allows you to explore without being harassed, and worry less when being chased by Mr X.
12. Shoot zombies that are on the ground! Most of them reanimate. Beware that there are about 5 in the game that will not reanimate until you do a certain action (puzzle or pick up item).
13. Shoot zombies in the knee to make them fall, then the head to kill them. They take more bullets on hardcore so make sure you have room to move backwards while shooting.
14. If you have to heal, use first aid sprays in the early part of the game. Always combine R+B+G and save them for the later boss fights and sewers since they also reduce damage.
15. I know I'm repeating myself but if you get hit outside of boss fights, reload instead of heal if possible.
16. Take your time! Time doesn't affect this achievement and only matters if trying for infinite smg, rocket or minigun, which if you are then you're insane.
17. Try to use only the pistol on zombies. There are 3 or 4 that require a shotgun shell to the face but that's it.
18. Ignore the matilda and it's upgrades.
19. The first Birkin fight is possible to beat without taking damage if you are patient. Run until he starts swinging, get in a couple shots, then run away.
20. On the second Birkin I used 9 magnum rounds, the pistol, and the crane twice.
21. On the third Birkin fight I used the shotgun for his outer eyes, then the magnum for his stomach eyes. Final phase I ran and used pistol. If you heal more than 4 times reload.
22. Tyrant fight- ALWAYS run in a wide circle around the platform. Start the run before he gets too close. Stand in a corner, shoot, then run in the shape of an L to corner diagonal from you. When rocks drop, use as a wall to get another shot in. I used all 400 of flamethrower, then shotty and then magnum. Beware it took 2 shots from the rocket launcher for me on this difficulty!
23. In Nest, burn plants till black or they will come back alive! Burn until they fall, then when fire goes out shoot a short burst and they'll catch for again and flare up, then turn black.
24. Best to save high grade powder for large gunpowder to get the most Shotty shells. Also I noticed the game has 50/50 chance of giving 5or6 shells when combining. Best to wait to combine until AFTER saving, that way you can make sure you get extra shell.
25.To give you an idea of items-
*Tyrant fight I had
Magnum-7
Flamethrower -400
Shotty-8
2 grenades
Pistol
4 healing RBG
Power plug
*Beginning of Nest
8 ribbons. 14 magnum. 600 fuel. 26 shotty. 2 first aid.
6G+B+R . 2G+R. 2G+G+G. 6 combat knives
Hope this helps you get the achievement! I was dreading this playthrough but once I got going I had more fun than I did on standard.