Will you be putting a Holster on the belt? If so, add a couple inches to the length or it won't fit. I have a 38 inch waist but the cartridge belt I use for Cowboy action shooting is 44 to the center hole with a left and right holster. Just want to save you some grief .
Not sure where you're located, But I get all my cast bullets from here, Good prices and great service.
https://bulletsbyscarlett.live-website.com/
Tell her I sent you.
A surefire way to remove the carbon ring is to shoot a couple cylinders of ammo loaded with a full charge of Black Powder. then clean and oil as required.
As mentioned, Lee makes a die set that covers .38 Short & Long Cold,they are reasonably prices too.
https://www.titanreloading.com/product/lee-38-shortlong-colt-3-die-set-carbide/
I have a friend that has loaded 25-20 ammo that he's looking to sell,I'll try to get in touch with him if you want me to. He is a fellow cowboy action shooter.Let me know if you want me to contact him.