Bravo2,
I havn't used Tubbs kit per say,but have been firelapping using abrasive compounds impregnated on bullets for years now.
The process works to cure many problems caused by rough bores that werent properly lapped at the factory/maker.
However they are NOT the answer for many other problems,and wont do much in a chrome bore.
As far as damage goes,properly firelapping a bore will cause NO damage,and will only cut about .0002 from the bore dia. in the first 4-8" of the bore.
If you are having problems with copper fouling due to a rough bore near the muzzle(Where most copper fouling occurs thanks to jackets heating up from friction) firelapping will help some but not cure the problem.
Only proper lapping with either a "Soft Lap" tool or lapping with a cast lap will help.
Often,factory sporting rifle barrels will respond favorably to firelapping as they are Hammer forged,and not finished to the level good quality aftermarket barrels are.
Why is it that you are considering firelapping???
Hope this helps.
S-28