It's baked on polyester based coating. It's tough as nails (you literally can smash a bullet flat and the coating still adheres), eliminates leading and makes the underlying alloy's hardness relatively un-important (you can use soft muzzleloader lead-when coated- at 1500fps with no problems). It's also very slick and feeds well. For my purposes, I've eliminated my use of soft lubes as the powder coat is far superior for cleanup.
One disadvantage is that it does not properly soften and clear fouling during black powder use. So if you want to stick with the holy black, avoid powder coated bullets.