The invention concerns the adjustment of the linear distribution of an injected shearing fluid, during casting, through a slot (20) provided in the cooled metal body (1)-refractory riser block (14) interface of an ingot mould for continuous metal casting charge and emerging along said ingot inner periphery, the latter being provided with clamping means for adjusting the slot thickness. The invention is characterised in that it consists in "cold" injecting through said slot (20) a regulating inflammable fluid, which is ignited on its exit from the slot, and in acting on the clamping means (25, 26, 28, 29) such that the height of the flames (39) coming out of the slot (20) is substantially constant along the whole ingot inner periphery. The invention provides the advantage of an accurate and lasting adjustment of the injected flow rate without requiring the adjustment of the injection slot thickness. The invention is applicable to continuous steel charge casting in particular.