Compare the cradle / recoil mechanism with:
Craddle and recoil mech are definately different altough probably of similar age and construction. The recoil of a high velocity 50-57 mm would be comparable to that of a medium velocity 75mm.
The point about only coastal guns needing a high velocity in early 20th century is valid, but the carriage would appear awkward for engaging a fast moving torpedoboat - or tank - if it is a later combination of barrel and carriage for anti-tank use.
Perhaps just a test rig for an experimental high velocity gun?
I was really referring the to square thingey under the barrel with the part sphere on the front, it even has the same cut outs for whatever it is called on either side of that.. Then look at the line of rivets just behind that.
I am not saying that the whole mechanism is the same, but it would appear that someone has decided to include with a barrel and breech mechanism onto a 7.7cm FK 16.
Perhaps experimental, well, yes, probably.
The rest of the cradle and carriage has come from somewhere else, obviously.
Then look at this:
Check wheels / tyres, breech handle, traversing (or is it elevation wheel). Same line of rivets under the barrel. Similar bar behind the beech on the carriage. The hoop at the muzzle would also seem to be similar.
So the original gun noted would seem to be a hybrid test weapon, using the carriage and much of a medium howitzer with a longer and smaller barrel inserted. This would not be a difficult thing if only used for tests, as the original chamber could be used, perhaps to see just how fast a medium calibre howitzer case and charge could propel something of around 57mm.
Edited by DougRichards, 18 March 2019 - 2307 PM.