Originally Posted by funugy
I dunno if I would trust it. I would suggest doing research to find out what the liner is made of, MSDS, flashpoint, etc. before leaving it in place.
If it were me, I'd do everything I can to get that liner out of there and get it to bare metal.
If it doesn't wire brush well... it may have epoxy content in the "red" coating for durability... I would agree with Funugy that you should look into the MSDS before cooking on that... or better yet, scrap it for another barrel.
If I had this to do over again... I would seriously consider the extra cost in buying a new, unlined barrel over sandblasting or grinding... takes a lot of time.