I'm an FFL, and ship long guns- and recommend the same to customers sending to me- to use USPS Priority Mail, with signature required.
It's not only cheaper (shipping UPS from the east coast to Cali costs a small fortune), but gets there in 2-3 days- faster than UPS in most cases.
Insurance is also available at a reasonable cost. Sending a rifle or receiver for service work to a licensee (FFL ) can be done legally with USPS with no special requirements.