Case trimmer cutting groove inside my necks!

[Ol` Joe]

Unless they are at or over max lenght leave them be. You don`t need to trim to the "trim to" lenght every time they excede it. The only time you should trim cases under the max lenght is when you are crimping and need equal lenghts for consistant crimps, or are loading from bench rest compatition and want even bullet pull, something that will never show a differance in a factory hunting rifle.
I had a RCBS trim pilot once that scored a light grove in the mouth of my cases. I found the edge of the shoulder where the pilot tapers to full diameter was sharp/burred. I took a piece of 800 grit emery I had laying around, and touched it "lightly" to the shoulder while turning it in my dremal tool. This cured my problem and I`d bet is what will help yours. Don`t turn down the OD of the pilot as this is what keeps the cutter running straight in the case. A sloppy pilot fit will cause other problems then a stratch in the cases mouths.