I think a pit would have to be really deep to cause barrel failure. I had a .410 with an extremely deep pit on the outside of the barrel underneath the forend. .410 pressure's for 3" shells normally run around 11,000psi and if any shotgun barrel should have failed due to pitting I would have thought it would have been mine, but it never did even after I'd fired 100's of shells through it.
Steve

Approach life like you do a yellow light - RUN IT! (Gail T.)