Easy, brass is a really soft material, dings are typically inward, so no case expansion has occurred so as to allow it not to readily drop into the chamber. Those inward dings will "iron out" up application of 45-52,000 psi in the chamber upon firing, fully supported by the barrel steel. If the case is too fat or oval in such a manner it wont fit the chamber, thats a different story, bolt energy may not be able to shove/form the case well enough into the chamber to allow bolt lock and firing to happen (remedial action drill needed).
If it really bothers you, go buy a "case gauge" and drop all your rounds, rather than feeding them into the rifle inside your residence.
I have fired many of those range pickups I find where the round has had the bolt lug "skid" the length of the case, leaving a long inward groove.