I have been experimenting with the Liberty Bricks as well and from what I can tell, they do not expand very much. With the exception of last night, I have mostly used them to fill in the gaps when I reload to increase my burn times. So far so good. BrotherBart's description of them as a lump of hot sawdust is good. They remind me of a lump of steel wool that has been lit with a battery.
Last night I lined up a row of 10 bricks on the bottom of the firebox and stacked wood on top as I normally would. This morning I came down to a warmer fireplace and a much bigger bed of coals with a bunch of little coal soldiers lined up still glowing.
Soon I want to do some burn runs with just the bricks. I am a bit nervous. From all my reading here, I have come to know that you need to respect the energy in these bricks and don't want to overload my fireplace. After seeing the space the row of 10 bricks takes up, I could easily fit 60 in my 7100 without touching the burn tubes. Not going to do that though. I have no desire to burn the house down.
(On a side note, my kids think the unburned bricks look like Spam that has been plopped out of the can. I agree.)
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