Shiny Silver Sphere seen for about 10 minutes in rural North Mississippi circa 1975

It was around October 1975 in rural North Mississippi, four miles north of Batesville. I was 16 years old at the time and was walking along the edge of a soybean field with my trusty .22 rifle squirrel hunting.
 I heard a very loud high pitched buzzing sound (like a cicada in the trees--which it may have been) but then everything was silent--even the birds. I looked up over my shoulder and saw a silver sphere just hovering about 300 feet above the ground and 1/4 mile away. It just stayed there. I thought, "hey look, a weather balloon." but there wasn't anything hanging from the bottom. Not a weather balloon. No gondola, so it also wasn't a hot air balloon either. It was just there hovering silently.
 Here's where I acted like a typical teenager. The .22 had a scope on it, so I looked at the sphere through the scope--looked like a shiny silver ball. I decided, "what the heck" I squeezed off a shot thinking if it was a balloon, I would be able to retrieve it. It hovered for a few seconds more then slowly drifted up and out of sight. There were cumulus clouds in the sky that day and the sphere was going along the edge of them rising in a slightly erratic fashion. But I was able to keep it in sight while it rose due to the contrast of the white clouds.
 The thing that still makes me wonder to this day is how readily I accepted what I saw and how I felt no alarm
Witness indicates that date of incident is approximate.  PD