...The dent starts from inside the barrel and is going outwards...
Uh...that does not seem right. If the barrel was dented from the outside in, it would have been the result of dropping, bumping or some other accident. The gunsmith should be able to fix those kinds of dents.
However, what you describe is likely the effect of firing with something partially obstructing the barrel. Have the gunsmith advise if the structural integrity of the barrel has been compromised...it may not be safe to shoot anymore.