go with mil-9954-13 size 13 will give u a satin finish and surface roughness will be around 25 to 30
well i dont know your machine of blasting but if it is suction and u use staight long nozzle u can go with 40 psi max 6" off the part and angle 45 degrees
note if the finish is not accepted u need brighter go to mil-9954-10 will help
