Legal Question in Criminal Law in California

It is impossible to give any sort of meaningful answer without more information.

There are many laws regulating gun possession. Some are felonies, which carry a potential prison term, and some are misdemeanors punishable by up to a year in jail.

You also mention that he isn't on probation, but you don't say whether he has a criminal record. That makes a big difference, too.

For example, a gang member who has a lengthy felony record and gets caught with an illegal machine gun will be treated much more harshly than a hunter who forgot to unload his rifle or shotguns, and illegally drove with loaded weapons in his car.

Please understand that this is a general discussion of legal principles by a California lawyer and does not create an attorney/client relationship. It's impossible to give detailed, accurate advice based on a few sentences on a website (and you shouldn't provide too much specific information about your legal matter on a public forum like this, anyway). You should always seek advice from an attorney licensed in your jurisdiction who can give you an informed opinion after reviewing all of the relevant information.Please understand that this is a general discussion of legal principles by a California lawyer and does not create an attorney/client relationship. It's impossible to give detailed, accurate advice based on a few sentences on a website (and you shouldn't provide too much specific information about your legal matter on a public forum like this, anyway). You should always seek advice from an attorney licensed in your jurisdiction who can give you an informed opinion after reviewing all of the relevant information.