Just an idea to present.....
On my 520 I use the short auger and 55 gal plastic drum.... for a number of reasons...
But.... there is one place that we deliver coal to, that in my mind is the idea set-up for a big bin. They built the bin out of cinderblocks, and at the bottom there is about a 1 foot by 1 foot hole. The bin has sloped sides covered with sheet aluminum, and when the coal slides down through the hole, it enters into another small cinderblock box that is app. 1 foot by 1 foot with no top and then the long auger enters the bottom of this box.
The big benefit to this..... Most rice coal these days is generally pretty clean, but never any garuntees. This is a six ton bin, and if something would plug the auger, you only move about 25-50 pounds of coal. I sure as hell wouldnt want to dig out a six ton bin to find the auger at the bottom.
Just a thought... Im sorry if that is clear as mud. I am sick as hell with the flue (pig flue maybe?