How about a ceramic barrel liner? Don’t have time to look up the melting points, but I wonder if a metal barrel could be cast, or even forged, around a ceramic liner. Would be complicated and expensive, but maybe worth it.
I haven't kept up with ceramics but just took a quick look around and it does appear that technology has advanced to the point that some form of ceramic/cermet or other advanced material will go into the barrel of this new weapon.