The gun they were shooting was the Model 1890 (like the one in Cannoneer's pictures), not the Model 1885. You can tell because the model 1890 barrel jacket extending forward of the trunnions is shorter than on the Model 1885 which also has a barrel sleeve that extends further up the barrel. The gun was leaking gas badly at the breech because the obturator head was visibly damaged and the fact that they were using reduced loads that probably were not producing enough pressure to seal the breech.