Martin, 140gr. is not a double charge in a well made 12 bore. 2F or 1F should be used in the 12 bore with round balls, by the way, as they develope much less pressure and a slower pressure rise than 3F. It is possible your 3F in Argentina is not as strong as GOEX or Swiss is here.
: 2 normal charges in a 12 bore smoothbore, shot with round ball, are 5.5 drams at 150gr. and 7 drams, at 191gr. The was also a light load of around 115gr.
: I have used both these charges in 2 3/4" plastic shells in my double 12 smoothbore with round ball giving proper regulation and good accuracy.
: The 7 dram load kicks pretty hard. One must 'steel' oneself against the 'hit'.
; I know of a couple guys with 12 bore Pedersoli double rifles who use up to 175gr. T-7 fake black powder.