This is probably not going to be believed, but here goes...
I was once loaned a muzzleloader percussion, that was extremely rusty, inside and out. I think it may have been a Thomson Center, but am really not sure. But the barrel was a Jukar made in Spain, that I do know. This rifle was worn out. Shoving a ball down the barrel was an experience, since in some places it was tight, and in others, almost fell down the barrel. It was obvious it had been not properly cleaned in years of use.
When I first got it, and shot about 20 rounds through it for practice, I swore I would declare the barrel unsafe, just because of the feel of the ball going down the barrel. However... The more I shot it, the better the accuracy got. It still doesn't make sense to me that such a rusty, pitted barrel should have any accuracy. Yet it did. In fact, I used that gun exclusively for over a year of hunting rabbits, taking many with head shots at over 50 yards.
But toward the end of that year, the barrel really started to show it's level of neglect. I always cleaned it after every shoot, but I think I was finally getting the crud out of it... lol. But it shot great until the time I returned it to the owner, and told him not to shoot it... I needs a new barrel.
My point is, don't give up on a pitted barrel... Try shooting it first. See how it reacts. See if it is consistent. A lot of times, we are seeking perfection where we should be seeking satisfaction instead.
