I'm sure he'll survive. Doesn't change the fact that anyone who leaves an assault rifle (I just forgot!) on a bench at a public range and goes home without it, whether it's me or you or Graves or rondog- is having a moment of total irresponsibility. Too busy talking or fantasizing.
I'm sure the op would freely admit to that. It's not personal. It's just the 2nd one I've read about in the past month. Check your area before you turn the key! A very expensive lesson that I'm sure he will never forget. Sometimes those are the best.