Lyman sizing die scratches

[mold maker]

I was half way through 3k 9mm cases when scratches on the cases started appearing. These were previously deprimed, and citric acid cleaned, with a final polish with cob and Nufinish. They are like new.
I've had the dies since the 80s, but have very seldom used them.
The dies are chrome plated. Could the plating be breaking down.
Anyone else noticed this?
An Email to Lyman has met with deafening silence.

[EDG]

Steel die or carbide?

Actually the problem is solved the same way regardless of the die material.

The die probably had brass stuck to it by cold welding - called galling. This is due to a lack of lube. It can happen even on carbide dies.

Clean the die with Hoppe's #9. Let it set submerged over night if you have time and enough Hoppes. Beware that Hoppes can strip plating too.
You could wad a patch and jam it into the die then wet just the inside with Hoppe's.

Then polish the die with 400 or 500 grit silicon carbide paper (wet or dry paper) used wet with a light oil. Spinning it in a lathe is the best way to do it.
Otherwise you can split a .250 or .312 wood dowel with a coping saw. Insert a strip of 400 grit and spin it wet with a drill motor.

Then clean it thoroughly and proceed. Just use more or better lube to avoid the galling.

[Char-Gar]

Your dies are dirty. Sometimes it is as simple as cleaning with a solvent on a cloth. Other times they have to be polished to get out scratches left by grit.

I chuck the die in the head stock of my lathe with a bore mop in the tailstock chuck. I wrap the mop with strips of paper shot towels to get a good fit and coat the paper with Mother's Mag Polish or any other good metal polish. Then with the die turning, I run the paper clad mop in and out. I finish with a good cleaning of the die.

If you don't have a lathe, you can use a drill press or even a hand drill. I have never yet had a die continue to scratch cases after this treatment.

[dudel]

I was half way through 3k 9mm cases when scratches on the cases started appearing. These were previously deprimed, and citric acid cleaned, with a final polish with cob and Nufinish. They are like new.
I've had the dies since the 80s, but have very seldom used them.
The dies are chrome plated. Could the plating be breaking down.
Anyone else noticed this?
An Email to Lyman has met with deafening silence.

Your dies are dirty. Think about it. If you scratched the die, you would have removed metal from the die (scratch goes below the surface of the die). How does removed metal in the die, remove metal in the case?

You have some grit in the die which is scratching the brass. I normally wrap a patch around a brush of proper caliber, put some Hoppes on it, then scrub the die (after removing the decapping pin). You'd be amazed how dirty it comes out, even with clean brass.