Best coal for a 96/97 coal loader

I just finished restoring my 96 pre war coal loader and tried using it for the first time. The coal that came with it (1930’s vintage I am positive) is realistic enough looking but it has many small pieces that want to jam the trap door track and keep it from closing. What are other folks using to prevent this from happening?
Pete

I believe that the new Lionel Coal will work better that the older stuff. It seems cleaner to me or perhaps newer just translates to cleaner.