I figure, guess really, that they do see some fins and a certain amount of reshaping (I don't like the word, slump). I agree that if they are uniform- my straight down the tube- the worst they will suffer is a change in balistic coefficient. 
All kinds of things are altered in the use of. I don't know it you'd call it damage, but it was a convenient word to use. Further, its just me making an observation, and not intended to get anybody too upset. Getting lucky with accuracy happens more often than any other way. Empirical.           carry on gents.

Just couple thoughts to add to the stew pot.   Considering that the heeled-bullets, and to some extent the stop-ring bullets, have technically sub-groove diameter bases. But if if the nose and the  segment of the bullet ahead of the case mouth fits the bore properly.  and if the bullet enters the rifling pretty straight, and any "blow-by" is adequately sealed off, they seem to shoot pretty straight.

I think the issue with the "fins" might be that if the 'dynamic"-base is irregular in the first microsecond when the bullet exits the muzzle the pent up gases behind it in the bore might kick the bullet a bit sideways and disturb the flight.  Perhaps any displaced lead is not forming "fins" but just getting wiped back into the grease grooves.   

I also shoot a lot of archery and target archers are finding that pretty seriously point heavy arrows shoot just as accurately as the long-accepted "perfectly balanced" arrows do, and in some cases with hunting arrows are actually more accurate

What do you think caused the 44 1/2 to be so inaccurate Joe? Seems many shooters today love tapered or choked bores?

Isn't six thousandths a lot more than the usual? I thought they normally only have half a thou, or a little more. Just askin', never had one. At least that I knew about