It sounds like a barrel obstruction (probably a bullet) was shot out, bulging the barrel. Usually the bulge is enough to interfere with slide movement, so someone likely enlarged the slide hole or filed down the barrel bulge.
I doubt the gun will blow up; usually the bullet just expands a bit then is sized down again, but if the previous owner was aware of the problem, it was not very ethical to sell the gun without informing the purchaser.
As a practical matter, you have little recourse and walking away may be the best bet. If you want, try
www.gunpartscorp.com for a new barrel.
Jim