Not quite true and the "Constructive Possession" discussion is not complete "FUDD."
To start with, you are completely correct that California's "Assault Weapon" statute does not include a "Constructive Possession" clause. But please do not be so naive as to believe that the lack of a "Constructive Possession" clause makes such possession legal. Remember that this is California, and the prosecutorial legal shenanigans run quite deep.
Where your argument goes into the toilet is with the California Court of Appeals 2013 decision in People v Nguyen. That case started when Mr. Nguyen was caught with the unassembled component parts of an Assault Weapon. The nice Orange County District Attorney charged Mr. Nguyen with the "Attempted Possession of an Assault Weapon." The DA could not charge the primary offense because the parts were unassembled, and (as you have pointed out, the AW statute does not include a constructive possession clause), the elements of the primary offense were not present. But Penal Code section 664 makes the attempt to commit the primary offense punishable, and that's the route that the nice District Attorney took. Mr. Nguyen was convicted and sentenced to six years.
The Court of Appeal basically found that there was no innocent purpose to the possession of the component parts other than to a some future point, assemble them into an Assault Weapon, and on that basis the attempted crime was complete.
The court gave an interesting treatment to Mr. Nguyen's attempt to argue the "Rule of Lenity" in his defense. In simple terms, the "Rule of Lenity" provides that if the ambiguous facts of a case can be added up to an innocent conclusion, and also be added up to a guilty conclusion, a criminal court must add them up to the innocent conclusion. In the Nguyen decision, the court discounted the possibility that Mr. Nguyen had an innocent purpose to the possession of the AW parts - "the rule of lenity applies only if the court can do no more than guess what the legislative body intended; there must be an egregious ambiguity and uncertainty to justify invoking the rule.‟
So, at the end of the day, even though there is no "Constructive Possession" clause in California's AW statute, Mr. Nguyen went to prison for six years for what was essentially the constructive possession of an AW.
You left out the premise to what led to the arrest of one of the most retarded CA gunowner.
A. Background
Defendant was the owner of an auto repair shop. On March 17, 2010, Police Officer Brian Chapman, on assignment as a detective with the Orange County Auto Theft Task Force, went to defendant's business premises. Chapman informed defendant that he and other detectives in attendance intended to search the premises. As a matter of standard procedure, Chapman asked defendant if he had any weapons on site. Defendant responded that he had a hunting rifle he used for shooting pigs.
Defendant led Chapman to a fully assembled .50–caliber DTC rifle. According to Chapman, the rifle was not one that would typically be used for pig hunting. Rather, he expressed the opinion that “even calling it an elephant gun would be an understatement.”
Chapman noticed that the rifle did not have a serial number or manufacturer name on it, so he asked defendant about it. Defendant explained to Chapman “that he had purchased the lower portion of the rifle that would typically have the serial numbers and manufacturing name off the Internet.” Defendant further explained that the lower portion of the rifle, or the receiver, was not completed when he purchased it. He had to “machine it” or drill holes in it in order to finish it. Defendant stated that he had completed the drilling process and put the pieces of the rifle together himself. Chapman dry fired the rifle and determined that it ought to be in good working order.
Defendant also took Chapman to some .50–caliber DTC ammunition—the ammunition that went with the rifle. In addition, he showed Chapman some .50–caliber Beowulf ammunition. Defendant explained that the .50–caliber Beowulf ammunition went with a different rifle he had rented for pig hunting.
After that, Chapman asked defendant if he had any other weapons, and defendant told him he was building an AK–47. Defendant took Chapman to a box of AK–47 parts. Again, the receiver had no serial number or manufacturer name. Defendant explained that he had purchased an AK–47 flat receiver, and he opined that when one purchases an AK–47 flat receiver that has yet to be bent into shape, one does not have to register the firearm. He pulled up the AK–Builder.com Web site on his computer and showed Chapman the AK–47 flat receivers for sale. Defendant had already bent his flat receiver into shape for assembly, by using a vise or a flat bending dye set.
Chapman asked defendant if he knew it was wrong for him to have and make his own AK–47. Defendant admitted knowing it was wrong.
Chapman said he met with Rocky Edwards, of the Santa Ana Police Department forensics services department. The two of them went through the box of parts and compared them to an AK–47 diagram and checked to make sure all the parts of an AK–47 were present, which appeared to be the case. He also met with Sergeant Greg Schuch of the Orange County Sheriff's Department, and the two of them compared the box of parts to the parts of a working AK–47. Having done so, Chapman opined that all the parts necessary to build a working AK–47 were present. Indeed, defendant himself acknowledged having all the necessary parts. It appeared to Chapman that at least one more hole needed to be drilled into the receiver before the weapon could be completed.
B. Charges
Defendant was accused of attempted unlawful assault weapon activity (§ 664, subd. (a), former § 12280, subd. (a)(1)), attempted possession of an assault weapon (§ 664, subd. (a), former § 12280, subd. (b)), possession of a firearm by a felon (former § 12021, subd. (a)(1), repealed by Stats.2010, ch. 711, § 4, p. 4036), and possession of ammunition by a prohibited person (former § 12316, subd. (b)(1), repealed by Stats.2010, ch. 711, § 4, p. 4036). It was also alleged, pursuant to section 667, subdivisions (d) and (e)(1) and section 1170.12, subdivisions (b) and (c)(1), that defendant was previously convicted of a serious and violent felony—a violation of former section 12025, subdivisions (a)(1) and (b)(3) (repealed by Stats.2010, ch. 711, § 4, p. 4036).