A Helblaster Volley Gun has the following profile and rules:

The Helblaster may fire up to three Artillery dice worth of shots in each of your Shooting phases. Roll one dice at a time. If a Misfire is rolled, roll immediately on the Black Powder Misfire Chart before rolling the next Artillery dice. If a May not Shoot result is rolled, this only applies to the current Artillery dice rolled. If a Malfunction result is rolled, this only applies to the current and the next Artillery dice rolled (if this is the third Artillery dice rolled this turn, the first Artillery dice the next turn is wasted). If a Destroyed! result is rolled, all previously Artillery dice shots this turn are still resolved before the war machine is removed. After all Artillery dice are rolled, resolve the number of shots as normal.