It might have been me on both counts! Yes I used the thumlers. It has the same size barrel as the harbor freight, but the sides are stepped rather than round. So if you think a half pound wouldn't be too much in the harbor freight, I'm sure this one did just fine.
I'll bet the reason green meal doesn't burn as quickly if it is due to problems with flame propagation as you say, is that there is too much air trapped within the super fine powder.
I will either screen it or corn it and see how it does.