C'mon Mark,
Having you in the thread, is already a satisfaction
Besides, i am also being a guesser; maybe not a so 'meager' one, as i am a food devourer and carry a 'fat' belly... oops, sounds more like a joke in my language
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I have had a local suggestion that it could be Dutch ... later captured by Portuguese, during these endless wars in the XVII century; i don't know.
One sure thing though is that, it was common practice in the period nations equiping their ships with foreign cannons ... captured and acquired.
You were right in that the trunions are placed well below the barrel center; but i have checked cannons from various origins, in a catalogue of the Lisbon Nany Museum (and not only), and i don't find this to be a pattern of a determined country.
The person who suggested Dutch origin also suggested the word ADMIRAL for the upper inscription left half; something i have already considered but, don't know why, have abandoned. But i reckon it is a heavy weight possibility.
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