How much it picks up definitely depends on the coal used and the depth of the coal pile. The original Gilbert coal was a lightweight, slippery plastic. The heavier and larger coal will not work as well, but even at its best the amount of coal per scoop is not great. That is one reason the 752A with the chute door was made. The bin could be filled while the trains were running doing other things.
I contacted Lionel about some of the coal packs that were mentioned by some dealers. Their response was that those packs were all for O Gauge accessories and I should have been looking at American Flyer parts. They gave me a part number 6409024086 COAL / BAGGED. Under my breath I asked, why wasn't that part number on the parts list!
I ordered some. I hope that its not the same cut up sprue scrap that came with the loader.