Barrel wear

[Old Gunner]

Jackie, it's my understanding that barrels can be set back as many times as the desired tune can be reached. Also, that these barrels continue to shoot very well.
Would you say this is often true?

Further notions of mine, stretch to understand why the 'combustion area' of a barrel destroys performance.
Aside from distance to lands(which may or may not be a problem), I'm left to think it's carbon related.
Could it be groove constriction due to carbon working it's way into steel?
If so, This would swage bullets below the rest of the barrel's groove. And at this point, and with this carbon being impossible to remove, performance could only be restored by re-chambering beyond the condition.

Just a suspicion, that you might measure.

Thats my understanding of it, though I've only read of this constriction with older barrel steels, I don't know if moder stainless has the same problem.
Apparently even a small setback will put the constriction zone back far enough that gas pressure remains high enough to give the bullet a secondary bumping up once past the constriction.

Set back barrels are still very evenly worn by friction, the wear so small that its difficult to gauge it. It is like a micro tapered bore, and set back barrels are known to shoot better than new ones as well as better than before the setback. The barrel is pre broken in with a new throat, the best of both.