Gas porosity is spherical in shape and the size can run spherical to the size of a pencil point.
Please check:

1. Check the burn out schedule being used; it may need a longer time at the top end
temperature to destroy carbon residues.
2. Check the air flow and exhaust on the burn out oven.
3. Check for investment residues left on metal being re-cast as it will decompose at higher
temperatures releasing sulfur compounds.
4. Check torch melting, check the oxygen/gas mix on the torch. Too much oxygen can
cause gas porosity.
5. Check the casting temperature, it may be too hot or you may have a bad thermocouple.
6. Check the reuse rate on scrap, the metal may have been reused too many times.
7. Check the flask temperature; it may be much too hot for the designs being cast.
If the metal stays molten too long in the flask it may absorb gasses.