Well I was at least wrong about part, if not all of this. If the Japanese din't have any record, what about other people of the same period?
To try to make some comparisons I started looking for anything on 16th century weapons and their manufacture. In several places I did find reference to arquebus being carried on sailing expeditions (Sir Francis Drake, etc.), and looking at pictures must conclude that there is a marked resemblance between the Japanese and European versions, including size!
For example:
http://www.nps.gov/archive/fora/arms.htm
I will be continuing to research this subject, and collect data :wink: