Penal Code 17(b) allows the court to reduce certain felonies, known as "wobblers," to misdemeanors. If you had a felony that was subsequently reduced to a misdemeanor, it will allow you to own a gun again -- with a couple of very important exceptions.
If you were convicted of a domestic violence offense, Federal law prohibits you from possessing a gun for life, even if the conviction was a misdemeanor.
As you note, some misdemeanors involving violent or assaultive conduct carry a ten year firearm prohibition. They are listed in Penal Code 12021(c)(1). If your felony is reduced to a misdemeanor, the ten-year ban for a misdemeanor would apply.
To be safe, I would strongly encourage you to get a Personal Firearm Eligibility Check (PFEC) from the California Department of Justice. They will tell you for certain whether it's legal for you to have a gun. Follow this link: http://ag.ca.gov/firearms/pfecfaqs.php
By the way, a dismissal under Penal Code 1203.4 (sometimes called an "expungement," even though it doesn't expunge anything) specifically DOES NOT restore your right to own or possess firearms.
1203.4 does not automatically, by its language, restore gun rights. It has limited value. A federally licensed gun dealer should be able to tell you whether you'll run afoul of federal laws.