@craigrice Use my fathers test. Make a small meatball. When you close your hand to a fist the sausage should ozz out between your fingers. If not add more water.

@jonathon yep, shorter horn makes sense. I am mech. engineer and there are two big things wrong here: the 9.5mm (3/8") stuffer tube and its length. Most of the problem, probably, ALL could be solved by using the diameter stuffer tube for 16 mm casings. There is NO advantage to going smaller, just disadvantages. Pressure drop(in this case back pressure on the cylinder / piston goes up exponentially as diameter is reduced.