Need info on this old artillery ammo

[fernando]

This would be a grenade for a 5 1/2" howitzer, those equiping the defence redoubts of the Lisbon protection against the third Napoleonic invasion (1810-11).
I assume this is a rational conclusion, as this bomb came with no ID evidence, but the its caliber and geographic source largely appoints to such direction. There were 5 1/2" howitzers in all countless redoubts and fortifications of this war episode.
Judging by its irregular exterior, it looks more like forged than cast, which i admit to be a nonsense inferrement.
Another surprising (for me) particular is that, its fuse orifice is rather narrow, comparing to the others i have seen, which look like measuring at least the double.
Noteworthy is that its hollow space is not completely empty; probing it with a stick i find that half ot its space has some kind of contents. Its colour looks too light to be explosive, i would say. I have poured out a tiny bit and set fire to it; it hasn't actualy gone aflame, but it didn't remain completely inert, forming a darker and thiker dust, hence giving me an ilusion that it isn't plain earth. It might as well be a mix of both, dust having penetrated through the hole and convering whatever contents is inside.
But my question is more focused on the hole width; does any of the members know how fuse devices functioned those days ? Are they (only) a wood plug containing a (regulable) match cord in a narrow hole ? Why the significant difference in the different grenade hole widths ? Different fuse systems ... narrow ones earlier, large ones later?
Your comments and possible referring illustrations will be appreciated.


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