I've been shooting a Darne R10 that has two pimple bulges in the left hand tube, for well over a decade. It has seen some hot loads in the past, but, usually doesn't anymore, as it is my prefered grouse gun, and I don't need hot loads in those woods.
The maker, in St Etienne, examined the gun, and told me to shoot it as is. Inspite of a healthy backbore some forgotten gun plumber did in the past before I got it, the minimum wall thickness on this gun is .064. There is a reason for that-it is a 65cm barrel gun, and in order for them to get these guns to balance well, heavy tubes, and an under-rib (uncommon on Darnes, usually) were used. Since the gun was a post WWII example, the steel was pretty good stuff as well. No worries, here.
Some bulges, matter a whole lot more than other bulges, it would seem, and it might have more to do with the rest of the barrels, than the bulge itself.
My point, long way around, is this-someone who knows something about shotgun barrels, and has the tools to examine all the details should have a look at it, and pronounce it fit to use as is (like my example, above) based on some measurements and knowledge of the gun. Kirk Merrington is a good example of someone who is more than capable of this.
Best,
Ted
