[Uncle Chip]

For example, here is a .223 and a 5.56 casing, both of them reloaded with .223 bullets.

Which brings up an interesting scenario:

.223 bullets in 5.56 casings -- which means the victims could have been killed with .223 bullets which then left 5.56 casings all over the place.

[Boogieman]

Yes, that is possible too.