BudsGunShop.com - Are these hard cast bullets coated with anything?

Yes, special "Black Cherry" coating. Instead of copy/pasting the info. Check out all you need to know on this round below.
https://underwoodammo.com/10mm-auto-220gr.-flat-nose-black-cherry-coated-hard-cast-hunting-ammo/

Hi Thomas and welcome. They use Underwoods Black Cherry coating which is a hard Lubulox Coating. Very similar to what was used on the old Winchester Black Talons. Cheers, stay safe and enjoy!

Hi Thomas, "Underwood Ammo’s hard cast featuring a new “Black Cherry” coating. Equipped with new enhancements from our previous Hi-Tek coating. Our “Black Cherry” coating is a polymer-based compound; its thermal stability allows it to handle more than any other coating today. The coating will protect against gas cutting with a high degree of wear and abrasion resistance. The “Black Cherry” coating prevents lead to bore contact, thus virtually eliminating lead fouling. All 10mm firearms can safely function with this upgraded projectile. To include polygonal rifling (Glock)."
Coatings special features:
No plastic burning smell
Thermally stable
Resistant to weathering and chemical degradation
Strong mechanical and tensile strength properties
Self-lubricating
Able to withstand high pressure conditions
Able to withstand high heat conditions
High degree of wear and abrasion resistance
Reduced friction resistance
Good flame retarding properties
Coating prevents lead to bore contact thus virtually eliminating lead fouling
Shoot higher velocities without lead fouling
.
Stay safe & have a great day!