Delayed or denied?
I don't know if CA has additional checks and requirements, but the feds won't explain a delay, just a deny. Delays are usually the result of the computer not being able to answer the question and having to kick it to a human.
If the conviction could have carried a sentence of over one year, whether it did or not, you are a prohibited person (under federal law) and may not purchase a firearm.
If this is the case, get a lawyer for further help.