Have you tried limiting your possible causes down by removing the trigger? Pull the pin with the c clip that holds the trigger in. Still hard? Remove the position spring. Still hard? Remove the trigger group entirely and then remove the bottom half of the safety. If you got the far there is a bind some where. If you had a smooth safety at the first step, then at least you know your safety isn't the problem.

Maybe you already know. I'm on my phone so it's hard to read every post so if it's been discussed, I didn't see it.

Edit: I didn't see the thing about the bolt. Make sure your trigger is engaging the sear correctly. I could see the sear being malformed and that could cause bolt pressure to push the sear into the safety when it shouldn't be. Just an idea.