Recently an LEO that I know remarked about how he is glad that local thugs seem to greatly prefer using semi autos rather than revolvers, saying that a great deal of useful information can be gathered from the shell casings found on the ground after a criminal event, something that obviously does not happen if a revolver were used. That made me think that from a criminal's point of view, or even a non-criminal who would prefer for any reason not to have the police involved in a self defense shooting incident, that using a revolver or at least ensuring that the shell casings of a semi auto do not include fingerprints might be a prudent action. This made me wonder about how often such cases are found without fingerprints versus those with readable prints on them. Fortunately most criminals are not too bright so maybe this is not really a problem for law enforcement after all. But wiping down cartridges before loading in a magazine might also make sense by not having the cases contaminated with oils from one's hands.