Federal law- you may purchase a firearm from a resident of your state of residence
You may not purchase handgun in another state. You may purchase a LONG gun from a dealer in another state IF it does violate state law. CA does NOT allow their residents to buy at a dealer's premises in another state.
When transferring ownership of a gun across a state line (except for inheritance) the gun must go TO a FFL in your state of residence.
You have not been able to have a gun "shipped to your door" since 1968, unless it was sold by the CMP, or you have a FFL. (Or live on a remote island in Alaska, etc)
You really need to get out more often, bro!