R.I.P. Scout26
(g)It shall be unlawful for any person—[snip](3)who is an unlawful user of or addicted to any controlled substance (as defined in section 102 of the Controlled Substances Act (21 U.S.C. 802));[snip]to ship or transport in interstate or foreign commerce, or possess in or affecting commerce, any firearm or ammunition; or to receive any firearm or ammunition which has been shipped or transported in interstate or foreign commerce.
https://www.law.cornell.edu/uscode/text/18/922
Thank you. But is "possess in or affecting commerce" the same thing as private possession? I don't think it is but I wouldn't want to be the testcase, especially after Wickard v. Filburn
The key phrase is "who is an unlawful user of or addicted to any controlled substance ... "Regardless of what the state's laws might say, cannabis is still an illegal ("controlled") substance under federal law, therefore anyone who uses it is automatically prohibited from firearms possession under federal law.