I can tell for sure 1886 is not the year when this was build.
Around 1916 the Italian Army started using license build Mortier de 240 mm of Batignolles design. Later on a longer barrel was used, and this seems one with a longer barrel. it.wikipedia.org/wiki/Bombarda_da_240_mm
It seems that the steering wheel with their shaft are fixed to the barrel and that when it changes its angle of elevation, that shaft moves through the groove of the side plate of the support.
I do not know why they put that date, this "bombarda" was not in service in the Argentine Army, so I do not have more data.
The "Museo de Armas de la Nación" is a civil society that belongs to the "Círculo Militar" and possibly has received this mortar donated by the Army or by the Italian Government.
In general, the Museum respects the data provided by those who make the donation (but may have been a mistake??)
As seen in all these photos, the mounting of this "Bombarda" is different from those seen in other publications of other mortars of 240mm derived from the Dumézil-Batignolles (French "Mortier 240mm", 9.45 inch English Mortar or the American copy)
The traverse movement mechanism was on the turntable and consisted of a gear that it moved on a ring gear and it was rotated with a spanner in T, behind the block where the propellant cartridge is loaded (in the breech)
In this photo it is clear that the barrel rises when the upper gears move over the gear arch, but underneath it moves an axis with its steering wheel that does not operate any mechanism.
Can only be some kind of brake to the barrel for to does not move ??