Hi Nando,
With these kinds of bores i always try to get a lightsource (sun/lamp) to shine directly into the bore and take a picture from some distance by zooming in.. the quality would however not be great but still well enough to see if the bore is smooth or irregular
I also want to add to my previous dating that i have no clue if the lenght would affect the age period.
In my recent findings from manuscripts i find that even 14th century barrels can be quit long, but this is a rather difficult thesis because of the lack of drawing things to actual scale in those times