Case trimmer cutting groove inside my necks!

[Mills]

I own a RCBS trimmer. After I neck size my once fired brass, I'm having trouble with my trimmer guide fitting too tightly into my case. When I trim, I'm getting grooves inside the necks of my cases. It almost seems like my necks are too tight. I'm using the Redding S neck die with steel bushing. Did everything correct on determining correct bushing size, but like I said, when I go to trim, guide is very tight and it's leaving a groove inside the necks. What should I do?

Also, if my cases are longer than the trim to length, but shorter than max case length, should I even trim them at all? Just wanted to have them all the same length.

[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.

[Jack]

Ol Joe's given you some good advice about checking the pilot for a burr.
If the pilot proves to be smooth....

......."After I neck size my once fired brass, I'm having trouble with my trimmer guide fitting too tightly into my case...."
Try trimming before sizing- the case neck will be expanded from firing, so your trimmer pilot should fit easily.
Another trick you can try is to put a dab of lubricant on the trimmer pilot- that can smooth things up a surprising amount. Imperial Sizing Die Wax works great- just a tiny dab every tenth case or so- and I'm sure most other case lubes would work, too.

[Cossack]

If all else fails you could get the next larger size of die bushing or K&M makes a caliber appropriate case expander (I believe Sinclare markets them) that I found useful before turning necks down in one of my rifle which has a match chamber.