"If I know how to make silencers, alter a bullet's or a shells use marks, and so on, there must be at least a million others who do also."

*sigh*...there PLENTY of 'dumb' criminal types who do NOT know how to alter gun characteristics....we have to get any edge we can, and this WOULD allow us to trace the path of many guns...at least to finding where it was sold new, which often helps.