Looks a little short for an 06 to me. I am more on the line of 7.62 NATO (.308 Win for you civies). Blank of course. Also I don't believe the 06 blanks have the elongated neck. I am sticking with 7.62X51 NATO.
Thanks for all of the help - the blanks from military training actually make sense. They were found with his fishing (not hunting) gear, so it would appear that he picked them up while wetting a line in the Idaho mountains. Mystery solved!