I don't know if that would be considered consumptive testing on not. Would there be blowback from shooting a corpse?
My personal theory on the missing bullet is that KK might have used the gun to shoot KB's phone in an attempt to destroy it at the Gorge near Gooding, ID (after sending those text messages but before returning back to her house to burn the remains of the phone). That could have stopped it from pinging all the way back to her house but it might not have destroyed the phone enough for KK's liking. One reason I'm thinking this is because I can't reconcile the idea of tossing KB's keys in the gorge but not tossing a disabled phone there too. But if she shot the phone and then wasn't sure if that destroyed it enough she might then decide to burn it as a plan B.
There was a case in Florida where a cell phone actually stopped a bullet and saved a clerk's life and this is what the phone looked like (see link, photo won't copy here):
Cell phone blocks bullet in Florida shooting
I'm sure that most people would not know off the top of their heads how well a phone would take a bullet. If I were trying to destroy a phone beyond all chance of recovery of any info on it by shooting it and I saw the above results I would change my plan to something that would do more damage.
MOO.