Recent spree-killings have strengthened criminological commitment to resolving the ever-looming question of how best to prevent criminal gun-fatalities (i.e., effective “gun control”?), but the U.S. Supreme Court held in the case of “Heller v. The District of Columbia” that the 2nd amendment guarantees the individual right to “keep and bear arms”, a ruling which renders traditional gun-regulation strategies (i.e. the handgun bans, “assault weapons” bans, etc.) both legally tenuous and politically sensitive, but which also then leave sentencing enhancements for gun-crimes as perhaps the most probable alternative gun-intervention. However, a recent National Academy of Science (“NAS”) Report has raised technical concerns about much of the most widely cited and extensively reviewed gun-intervention outcome estimates, and it concludes moreover that both the validity and reliability of the results are variously questionable overall. This study, then, adjusts for those technical concerns to re-estimate accordingly the effects that sentencing enhancements for gun crimes may exert on homicide rates and gun-homicide rates, respectively, in 20 major cities across the U.S. between 1970 and 2005, and it finds that one type significantly reduces gun-homicide rates, but that none detectably reduce total homicide rates