Realistically for us here in Cali, your options are pretty much wall hanger or gun buy back. California has it's own laws surrounding "ghost guns" and all that, so I'm assuming the new ATF rules really won't affect us here much.
And actually that specific federal definition was adopted into our state code. I actually misspoke when I said they made the definition per the supreme court case, they made the definition in 2022 and it was upheld by the SC with Vanderstok
Cal. Code Regs. Tit. 11, § 4303
(a) For purposes of this chapter, the following definitions apply:
(1) "Federally regulated firearm precursor part" means any firearm precursor part deemed to be a firearm pursuant to Chapter 44 (commencing with Section 921) of Title 18 of the United States Code and regulations issued pursuant thereto, and, if required, has been imprinted with a serial number by a federal licensee authorized to serialize firearms in compliance with all applicable federal laws and regulations. (Pen. Code, § 16519.) As of August 24, 2022, the "regulations issued pursuant thereto" are sections 478.11 and 478.12 of Title 27 of the Code of Federal Regulations (August 2022), hereby incorporated by reference.
(2) "Firearm precursor part" means any forging, casting, printing, extrusion, machined body or similar article:
(A) that has reached a stage in manufacture where it may readily be completed, assembled or converted to be used as the frame or receiver of a functional firearm; or
(B) that is marketed or sold to the public to become or be used as the frame or receiver of a functional firearm once completed, assembled or converted.
"Firearm precursor part" does not include firearm parts that can only be used on antique firearms, as defined in Penal Code section 16170, subdivision (c).
(3) "Frame" means the part of a handgun, or variants thereof, that provides housing or a structure for the primary energized component designed to hold back the hammer, striker, bolt, or similar component prior to initiation of the firing sequence (i.e., sear or equivalent), even if pins or other attachments are required to connect such component to the housing or structure.
For a split or multiple part frame design, "frame" instead means the part of a handgun, or variants thereof, that has been designated as the frame by the federal Bureau of Alcohol, Tobacco, Firearms, and Explosives in subdivision (f)(1) of section 478.12 of Title 27 of the Code of Federal Regulations (August 2022), hereby incorporated by reference. One example includes the Ruger Mark IV pistol, in which the frame is the upper part of the weapon that provides housing for the bolt or breechblock.
(4) "Machining" means the process of cutting, drilling, shaping, indexing, milling, or removing material from a forging, casting, printing, extrusion, or similar article using a tool or equipment.
(5) "Readily" means a process, action, or physical state that is fairly or reasonably efficient, quick, and easy, but not necessarily the most efficient, speediest, or easiest process, action, or physical state. With respect to the classification of firearm precursor parts, factors relevant in making this determination include the following:
(A) Time, i.e., how long it takes to finish the process;
(B) Ease, i.e., how difficult it is to do so;
(C) Expertise, i.e., what knowledge and skills are required;
(D) Equipment, i.e., what tools are required;
(E) Parts availability, i.e., whether additional parts are required, and how easily they can be obtained;
(F) Expense, i.e., how much it costs;
(G) Scope, i.e., the extent to which the subject of the process must be changed to finish it; and
(H) Feasibility, i.e., whether the process would damage or destroy the subject of the process, or cause it to malfunction.
In determining whether a forging, casting, printing, extrusion, machined body, or similar article has reached a stage in manufacture where it may readily be completed, assembled, or converted to be used as the frame or receiver of a functional firearm, the Department may consider any available instructions, guides, templates, jigs, equipment, tools, or marketing materials.
(6) "Receiver" means the part of a rifle, shotgun, or projectile weapon other than a handgun, or variants thereof, that provides housing or a structure for the primary component designed to block or seal the breech prior to initiation of the firing sequence (i.e., bolt, breechblock, or equivalent), even if pins or other attachments are required to connect such component to the housing or structure.
For a split or multiple part receiver design, "receiver" instead means the part of a rifle, shotgun, or projectile weapon other than a handgun, or variants thereof, that has been designated as the receiver by the federal Bureau of Alcohol, Tobacco, Firearms, and Explosives in subdivision (f)(1) of section 478.12 of Title 27 of the Code of Federal Regulations (August 2022), hereby incorporated by reference. Some examples include the following:
(1) for AR-15/M16 variant firearms, the receiver is the lower part of the weapon that provides housing for the trigger mechanism and hammer (i.e. lower receiver);
(2) for a Benelli 121 M1 Shotgun, the receiver is the lower part of the weapon that provides housing for the trigger mechanism; and
(3) for Vickers/Maxim, Browning 1919, M2, and box-type machineguns and semiautomatic variants, the receiver is the side plate of the weapon that is designed to hold the charging handle.
(7) "Variant" and "variants thereof" mean a weapon utilizing a similar frame or receiver design irrespective of new or different model designations or configurations, characteristics, features, components, accessories, or attachments. For example, an AK-type firearm with a short stock and a pistol grip is a pistol variant of an AK-type rifle, an AR-type firearm with a short stock and a pistol grip is a pistol variant of an AR-type rifle, and a revolving cylinder shotgun is a shotgun variant of a revolver.