Reloading dies if taken care of properly will provide years of service to their owner. Most dies are hardened and then micro-polished for that mirror finish many of the dies exhibit. Many of them are also treated with some type of rust preventative before they leave the factory floor.
The first step in taking care of your dies starts when you receive them. We advocate cleaning all new dies before you begin to use them. Beginning with your sizing dies; take the decapping assembly completely out of the die body. Flush the decapping assembly with a good degreaser (like Hornady One-Shot Cleaner & Dry Lube, Birchwood Casey Gun Scrubber or Shooter’s Choice Quickscrub III) and wipe the expander ball clean. The only part of the decapping assembly that should come in contact with your brass is the expander ball and the decapping pin. Pay particular attention to the decapping ball as it determines the final interior dimension (bullet grip) of your case neck. Make sure you inspect it after cleaning to make sure that the surface is clean and free of burrs.
Next, flush the interior of the die body out with some more degreaser. Using a pistol cleaning rod or a dowel rod, push a couple of wet patches all the way through the die. Then run a couple of dry patches through. Reassemble your sizing die and you should be good to go.
Taking apart your seater is fairly simple depending on the complexity of your seating die. A standard seater just requires you to turn the seating stem out of the die body exposing the interior of the seater. Flush and clean both the body and seater as described above. Benchrest sliding sleeve seaters such as Forster or Redding Competition Dies have a few more parts involved. Just make sure as you take them apart you know how the spring is oriented and how any other parts such as chamber sleeves or seating plugs are arranged. Any springs or threads can be wiped down with a very rag or patch lightly coated with a fine oil. Make sure you inspect the opening in the seating stem for debris. You can twist a patch and use the end to clean out the smaller caliber stems/plugs.
Regular maintenance of your dies should include their routine cleaning. Sizing dies collect excess lube off the cases and this lube can begin to build up. We have seen dents formed in the case shoulder from the hydraulic compression of the excess lube in the die when the case was sized. We recommend cleaning the dies every 500 to 1000 rounds depending on how frequently they are used and the cleanliness of your reloading area. My reloading area is in the same building (different room) as my woodshop and I have to watch the dust so I keep most of my reloading dies covered or stored away. I keep a cover over my press and scales as well.
For longer term storage of your dies, I recommend putting a light oil or rust preventative on them, especially if you have a shop that has a humid environment.
Although, we titled this article about reloading dies, I might mention a few details about your reloading press. Cover it with an old towel if you can when not in use or buy a cover if one is available. Make sure you wipe the ram off occasionally and clean the area around the bottom part of the frame where the ram comes through. Primer grit and debris builds up there and can begin to wear on your ram and casting as it accumulates.
Pretty simple stuff but often neglected by many of us. Take care of your reloading tools and most of them will last a lifetime.