Cutting a cannon ball in halves would never be my cup of tea. Something different would be to acquire a good fragment of a bursted grenade. 
I have a reasonable collection of these things and never had one still loaded. The only time i dug some contents from a 5 1/2" howitzer grenade i found no more than some residuals. 
I wonder if when the Brits came over for the Peninsular war (also) brought artillery ammunition; the examples i have from that period are not marked and are potentially Portuguese ... or some French. 
The ones i have with marks are a 15 HJH 75 (Herzog Julius Hütte) dated 1575 and a XVI-XVII century German clay grenade; the picture shown has a replica fuse; the proper one, not the original but a similar one offered by Michael (Matchlock) is too fragile and kept in a small acrylic case. 
The first and second ones in the first picture are stone 'pelouros', a German XIV-XVI century 17 pfund limestone and a Portuguese XVI century granite weighing 18 arratles. Number #3 and #5 are XVIII century 6" and 51/2" howitzer grenades later used in the Peninsular war. The second one in the second picture (set) is one of many hand made by Peter Pögl for King Maximilian. 
 
 
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