If a previously convicted felon wishes to obtain a firearm, is he permitted to obtain and possess the firearm?

We conclude that if a previously convicted felon desires to obtain a firearm, he should first challenge the validity of the prior conviction by a motion to vacate the conviction in the court that entered the judgment. (See Lewis v. United States, supra, 445 U.S. at pp. 60, 67, 100 S.Ct. at pp. 918, 921; Neal v. State of California (1960) 55 Cal.2d 11, 16, 9 Cal.Rptr. 607, 357 P.2d 839.) But he may not resort to self help by first obtaining and possessing the firearm, and thereafter try to assert the invalidity of the prior conviction as a defense to a prosecution under section 12021. ²

2. Effect on Sentence Enhancement