Thanks to the thoroughness of the Austrian Lieutenant Major Paul Sixl, who took all the photos you have been quoting and also noted the measurements of all these guns which were published in the Zeitschrift für Historische Waffenkunde, vol. 2, 1900-02, pp. 264ff., I can tell you that the wrought iron haquebut barrel no. 5
has an overall length including the socket of 99.8 cm while the barrel itself has a bore length of 79.7 cm and a caliber of 26 mm; the piece weighs 15.4 kg.
Telling by the place of your red number 5 which indeed marks the first in line barrel of the group, though, I am not quite sure whether you really meant that first barrel (which actually is no. 1 in Sixl's article).