Most people don't know what a bull barrel is when speaking of T/C Encores and Contenders.
Standard Contender barrels come in tapered and bull configurations. The bull barrel has no taper.
Encore barrels come in tapered, heavy and bull configurations. The heavy barrel has just a little taper while the bull has none. The bull barrel takes a special forend.
Though I've had many heavy Encore barrels, I've never seen a factory Encore bull barrel. As large in diameter as a heavy barrel is, I can't imagine that a larger diameter barrel would be of much advantage.