And I think there were a total of 12 shots - otherwise the killer(s) would have had to stop and reload, and I don't think they did that
While I don't believe their was any reloading done, why do you assume that the guns used only held 6 shots each? If casings were found at the scene then the murder weapons had to be either semi automatic rifles or pistols. Only a revolver wouldn't have left any casings at the scene. If the murder weapons were semi automatics there could of been numerous other shots. Do we know how many more shots that might of been fired that didn't even hit the girls????? For example I have an older model 22 rimfire rifle (semi auto) that holds 17 bullets. I have a 9mm semi automatic handgun that holds 15. I have an AR-15 that can hold 10-30 rounds depending on what magazine I'm using. Several .22 semi auto pistols can hold 10-12 rounds of ammo. I still believe the smaller weapon used could of been a .22 rimfire which is a gun that kids typically plink around with.