Without knowing what the propellant is and having it available, you can’t. Factories often use a propellant that is specially blended, (referred to as a noncanister grade powder) propellant that they usually won’t identify. Never try to identify a powder by its appearance! This can be extremely dangerous. Every year we hear tales of shooters who tried to duplicate a factory load by using the same charge weight of a powder they thought they had identified, only to damage their guns or injure themselves. Stick to the loads listed in recognized manuals.