Jackie Brown is known for making guns very quickly and inexpensively. Your dissapointing experience is, sadly, typical among JB customers. The tubing barrels are what he uses. Some have visible seams inside and are usually at the bottom. Opinions vary as to wether or not his barrels are safe.
My JB fowler does not have a visible seam, I stipultated to Jackie that it must not. But my 36" barrel as ordered came to me at 31" and with a host of other problems.
Do some searches on the forum for Jackie Brown for more information.
IMHO, the seam you have is probably safe. Having it on top where it can be seen is a huge dissapointment. Majorly ugly I would guess.
How old is the gun? Jackie is usually cooperative in repairing his guns.