I believe jhalcott and I are rowing the same boat. I put "bull barrel" and "standard barrel" into the same basket. A factory, standard barrel is a bull barrel. Or am I mistaken here? T/C used to offer an octagon barrel, but I believe that is a dead breed. And I'm not sure I've ever seen a tapered factory barrel in handgun trim (you did say 15").
The question I see here is custom shop or factory barrel? OTT makes a larger bull barrel then a factory T/C. Tapered anyone? in pistol trim? can't help with that one off the top of my head.