First death was in the room right before you enter the Church of Unitology to start Chap. 4. So, I saved right before that part to avoid a death, even though it was super early, I didn't want to die at the hand of the two exploders again. I died two other times before I made it to the same spot again and was able to save from trying to rush from the anger of dying the first time (beginning scene, lame! And also from the doors that fly off the train). It was at this point I thought I would never, ever beat it on Hardcore, but I kept at it.
After my first save in chap. 3, I had an amazing run where I didn't die at all and I saved it at the part right before the tripod nest where you blow up the canisters. After that I had another great run before I had my most painful death: right before the last brute where you go through the 3 tiered room with a ton of necromorphs. A spitter got me on the second floor, slowed me down, and some fuckass slasher raped me from behind that came out of a vent before I could retreat. I literally just sat there staring at the screen for a full minute. 3.5 hours lost...and only 5 minutes from saving...
So again in my anger I rushed, trying to go through those 4 chapters fast and died a bunch of times: at the two brutes, the decontamination room, the hall after the decontamination room, and some room where two exploders join the party.
Waited a day to play again and made it to the eye machine and saved. Died at the sliding doors in the no gravity room with the nest, then tried again and beat it. Ended up being the second longest achievement in terms of hours spent specifically on it to get (12 hours or so counting deaths). That hand cannon was worth it though, was able to finish Zealot in one sitting in about 4.5 hours.