He was even in LEGAL possession of a rifle in Wisconsin. See post above.
https://docs.legis.wisconsin.gov/statutes/statutes/948
948.60(c)(3) allows a dangerous weapon exception for minors over 16 to possess a rifle as long as the barrel is legal length.
*948.60(3)(c)
https://docs.legis.wisconsin.gov/statutes/statutes/948