When you're curing powder coating.
Used some Reynolds paper the first time I powder coated a batch of bullets and it worked great, bullets just slid off of it. Ran out of it so the next time I used some store brand that someone had given me a long time ago. It worked fine for baking cookies but definitely not for powder coating. It turned very brittle and crumbled like centuries old parchment and it stuck to each bullet, leaving a shard of paper that has to be picked off. Except it won't come off entirely and leaves a small strip right where the bullet contacted it.
Was trying to pick off those little remnants one by one as I sized them but that would take hours and you stll can't get all of it off anyway. So I'm just going to scrap the whole batch - three hours work and over 15 pounds of bullets, almost 675 of them by weight - and remelt them.
Lesson learned, don't use cheap parchment paper.
