After reading this entire thread I of-course found a barrel on craigslist and got working. The barrel I received held some type of food grade oil and had the common tan liner.
After cutting the intake holes (3 1'' holes) with a wood drill bit (don't do this) I burned out my drum with a pallet of wood.
I used a good strong brush and some 409 to try and clean the inside, but the black just won't come off. Some of the inside is black, some is almost bluish, and some is plain metal. Sticking my head inside it doesn't smell like anything, where as with the liner – it smelled like paint. It seems though that my burn would have definitely burnt the liner off.
I took a piece of sand paper and sanded some down to bare metal. It seems like the barrel just has a layer of black soot, like pre-seasoned? I don't have many tools and sanding the whole thing by hand seems like a pita...but I'll do it for safety if needed.
I took a picture of the inside. What do you guys think?