I've used this RCBS FL die in my 300 WM for several hundred rounds. About 20 rounds or so ago, it started putting verticle lines on my case necks. The scratches are pretty deep, I have cleaned the die and it was not dirty. Any idea what could be causing this or how to fix it?

Mine do it too. It may be some galling. I'm gonna Flitz the die body and neck

I might try some steel wool wraped around a cleaning brush tonight and see if it helps. Might put some bathroom scrubbing gel on it for added polish. It has to be galling where the expander is pushing the case neck against the inside of the die body.

How does this happen? Do you have the expanding plug all the way up in the neck region of the die?

Sounds like you might have got a piece of grit in there and now it has a burr. I have polished some out like that by using a wooden dowel wrapped with 600 grit paper and oil.Chuck in a drill press or hand drill.

You won't remove enough metal to make a differenc,but it will usually polish out the burr.

Steel wool isn't going to do anything excpt maybe clean it.

It could be as simple as some brass buildup. If one or two cases didn't get lubed enough the brass would be scraped off on the die which is enough to create that mark. Have seen it plenty of times.

Recently had a Redding competition die scratch some case necks too. I used that die for hundreds of rounds with no cleaning. Now I know better. I had to do some polishing with JB on a patch wrapped tightly on a bore brush, which removed it easily.

My 260 sizer die does it also.

Good thread...answered a question I hadn't asked yet.