A cannonball ... a pommel ... or what ?

[fernando]

Thanks for your input, Gentlemen
Indeed i though of all those possibilities, but the question remains that all they use round balls.
... Unless this is one of these atypical specimens for barrels with experimental bore sections, as recently discussed here ... in this case of octogonal section
I know that Professor Daehnhardt has acquired on of these from the source i got mine. I will try and find if he has an ace up his sleeve for this one.