how did i ruin my sizing die?

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I've been shooting a 6mm Comp Match for several years. I've loaded approximately 3000 rounds in that amount of time.
This past spring when I was loading up some practice rounds I noticed that my sized brass was coming out of the die scratched. The scratches are parallel to the axis of the case, and at several points around the circumference of the case. It had been a while since I cleaned the dies so I tore them down and took a look. There where huge brass streaks in the die. I cleaned the die, which ended up being a hassle. I had to use wipe out to get rid of all the brass in the dies. Then I hit them with break cleaner followed by One Shot cleaner/lube. I inspected the dies again. Brass streaks are gone, but I can see pits/burrs in the die body. Using a cotton swab you can easily feel these areas. I'm going to call Redding this week and see if they can hone that out and return the die.

My reloading procedure for this brass (after being fired) has been:

1. Tumble ( I think the latest bucket of media is walnut)
2. Anneal
3. Lube (Dillon or Frankford Arsenal lanolin type)
4. Size
5. Prime
6. Charge
7. Seat

What happened that I scored this die?
Was the brass not clean enough? Lube issue? Die not cleaned often enough.

I want to avoid this mistake in the future.
Thanks,
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[bigedp51]

Take a snug fitting shotgun cleaning mop, chuck it in a drill and apply J&B Bore Paste and polish the inside of the die.

I have never seen a die pitted on the inside, "BUT" I have seen brass sticking to the inside of the die.

Below is a bushing that the poster thought he had removed all the brass.

I would use a very strong copper cleaner that will curl your nose hairs if you sniff it and make your eyes water and apply it to the inside of the die first. This should remove the majority of the brass sticking to the inside of the die.

Cases that are excessivly polished tend to cause the brass to stick to the die.

You can also disisemble the die and place the die body in your vibratory tumbler with treated walnut media and polish the die.

Tech Line & Tips (FAQs)
https://www.redding-reloading.com/tech-line-a-tips-faqs/149-scratched-cases-causes-and-cures

Scratched Cases: Causes and Cures

A problem that customers occasionally encounter while reloading, is that of cases being scratched in the reloading dies. There can be many reasons for this condition to occur, but they are usually traceable to the level of cleanliness of both the dies and the cases. Generally speaking, almost all instances of case scratching can be traced to foreign material that becomes imbedded in/or adheres to the inside surfaces of the die itself.
As a part of their final processing, Redding dies are cleaned with an ultrasonic cleaner to remove any foreign material which may remain from the manufacturing process. This is the same procedure used to super-clean aerospace parts, hydraulic valve bodies, and the like.

Case scratching problems can usually be traced to the reloading area and some of the equipment that may be in or near it. A few guidelines that will help are listed below:

1.Keep the abrasive dust and particles from spent primers cleaned up and away from all equipment.

2, If you have a small bench grinder, it should be kept away from the reloading bench, preferably in another room.

3. Loading on the range, especially in windy or dusty conditions, can introduce cleanliness problems that can be hard to manage.

4. Case tumblers are another potential source of problems. While the cases may come out shiny, they will actually have a thin film of abrasive residue on them. Cases should be thoroughly cleaned and/or washed before going into the dies.

5. Nickel plated cases are often associated with die scratching problems. Small particles of the hard nickel plating may be present from trimming and/or deburring operations and can find their way inside the dies.

6.It is important to understand that foreign material does not have to be hard to cause problems. Brass chips from trimming and deburring can find their way inside the resizing die, where they can literally be welded to the inside of the die under the extreme pressures generated by full-length resizing. When this happens, the "brass against brass" action will gall the cases, leaving an apparent scratch. The condition will rapidly worsen as brass continues to build up.

Cleaning Your Dies

We are often asked, "How should I clean my dies?" The answer is to use the same procedures, with the same equipment and solvents, that you use to clean the bore of your rifle or handgun. Use the same diligence and effort as well, since the brushing and copper solvents will work well on any brass deposits that may have accumulated inside the die.

Another question that comes up is, "Can I do any internal polishing?" Again, the answer is, "Yes, with care!" The best arrangement is to chuck the die in a lathe, after stripping it down and removing the internal parts. Use #400 or #600 wet/dry auto body paper wrapped around a small wooden dowel. Keep the paper wet with a thin petroleum product with the consistency of WD-40 or kerosene. Using this method, you will easily be able to remove any foreign material or brass build-up from the inside of the die.

Since our dies are heat-treated to approximately 62 Rockwell C, you can polish for a long time without changing the internal dimensions. Do not use ordinary sandpaper or anything coarser than #400, as you will scratch the interior of the die surface and void the lifetime warranty.

It is very important to give the dies a thorough cleaning, after the polishing operation. They should be thoroughly washed, flushed, and wiped several times. Again, just as when cleaning your rifle, check the dies for cleanliness with several wet patches and then lube and dry patch them.

In summary, the name of the game when it comes to avoiding scratched cases is cleanliness! A little attention paid to keeping your reloading area clean, and periodically cleaning your dies, will insure that they give you years of trouble-free service.

 

[BiscuitsandGravy]

Another vote for bits of brass stuck in the die. We ran into that a few years ago with a 300BO die. YMMV.

 

[Hawkeye7br]

Usually the culprit is tiny bits of dust and grit from the tumbler. Once the die is scratched, it will always be scratched unless you polish it as described above. The burr you created in the die then collects the brass. The good news is that it's mostly cosmetic.