Jim,
somewhere, and it has been so long, I have heard, not a good reference, that a hole was cast in the partition partition was an open hole when the sand was removed. The incendiary mix was funneled in first, the hole plugged with a substance. probably wood, then the powder was measured in the top chamber through the fuse hole.
I normally don't post, I've heard "I heard". I want to say its from John Biemick, but I will call him to check.
It was Biemick, John advised Sam White about the plugged partition and it was in a 6.4 inch shell (100 pdr..). .John should publish his two books on C.S.A. and U.S. riflled ordnance. We would like images of the fuze/fuse to determine which, as not too many of the incendiary shells survived.
The Marines will probably have to drill from the side just below the to get at the black powder and a second hole along side the bolt to determine if the contents is powder or the mix. It is also a chance that the incendiary mix has cotton waste to assist in scattering the mix and in its burning. I'll bet he has powder from to to bottom. the mix, when filled with cotton is a job to clean out.
The illustration shows the original purpose of the base hole.
Thanks.
Regards,
John
P.S. John might be able to answer your question about the partition's position.
P.P.S. mixing black powder with the mix would destroy its normal function to burn than if it were dry.