Well - There are more bulged barrels around than people know, or admit. Normally the stresses at the muzzle are relatively low, a small fraction of what they are at the chamber end. An obstruction causes the pressure to spike locally, hence the bulge.
For me, I would have no problems shooting it, as the stresses are low under normal circumstances. If one wanted additional assurance, non destructive inspection for cracks or flaws would be the ticket.
If the rifle is stock military, I'd try to leave it as is. However, if you're not satisfied with the terms of purchase, the seller should be approached.