Reminds me of an incident when I was at Ft. Monmouth, where 2 gate guards (MPs) in the middle of the night were playing quick draw to amuse themselves - one wound up gut-shooting the other.

Under the heading of completely idle curiosity, I wonder if this is the same sort of thing?

I'd guess that they load/unload their sidearms in that "security booth" because of some silly rule requiring their guns to be unloaded at certain times or in transit to certain areas.