Very interesting idea. Thank you.  I have been thinking of making or buying some straight 24 ft long straight slant bar sections - sort of like a flat Apple gate feed ring - to use instead of guard rail.

Now add your idea of making it moveable in towards the center...

Given the moveable rail idea, I wonder about making the inside 12 ft wide rather than 8 ft. It would give me the opportunity to load 2 rows of 6 ft bales or 8 bales at one time in the center. As they finish what they can reach then move the rails in toward the center....  12-6" ft wide would give a little more working room with the tractor than 8 ft.  Reduce the outside eave overhang so could still use Garvo's basic dimensions and materials...

I could put the neck rails on rollers with guides and maybe even let the cattle push it in.  Would only have to load it half as often as for 4 bales... I wouldn't have to move the rails, let the cattle do the work.

Thank you jcs. I think this could develop over the winter into something.

Jim