At the risk of "boring" you all...

[Patrick Chadwick]

"70 cm, or as the makers would have said "28 Zoll" - not inch!

That was a really strong clue. If one takes the trouble to look up old weights and measures, one can discover that in 1817 the Hessian foot was officially defined as 30cm, and this lasted until (I think) 1871 and German unification. Since there were other "feet" at the time (Austrian, Prussian etc.) which were defined to 2 decimal places, the Hessian foot must have already been very, very close to 30cm indeed, making the Hessian inch 2.5mm, plus or minus a gnat's whisker. Once you picked up that, by using the word Zoll, I was hinting with a huge hammer that the inch in question was not an imperial inch of 25.4cm, you could have discovered that the 70cm could only be 28 Hessian inches. Nobody else's inch gives a round number!

Austrian inches were longer than 2.54cm. So the slightly odd 7-and-a-bit inch barrel length of my Gasser revolver is a straightforward 7 - in Austrian inches. Somewhere in a museum in Munich I once saw a roomful of "feet" from different states - even different towns!