For years I have wondered why these are not more popular..... https://www.youtube.com/watch?v=XpDVeXEeOdw
For you guys with tractors or other equipment with forks that can lift high enough, I believe this is the easiest way to fill feeders and if you don't have an over head storage hopper you could have the bulk corn brought to your place and fill as many bags as you want at a given time..... I think they hold 2,500lbs of corn per bag.
Just make a frame to both hold the bag while filling and a screen made of 1/2" wire mesh for the corn to go through as its filling into the bag and then you can have as many tons of corn ready to go pre screened.
Just use the forked equipment to lift it over the feeder and untie the knot at the bottom of the bag and when the feeder is full you can easily close the drop hole on the bottom of the bag and move onto the next feeder.
Word of advice though.... when your moving from feeder to feeder use zip ties to secure the knot tied in the bottom of the bag and simply cut and replace them after each feeder fill.
Buddy of mine had the dump knot come untied while driving around the back of his ranch and dropped 2,000lbs of corn in the middle of his road before he could get the tractor stopped.