Instructing the jury on Felony Murder theory of First Degree Murder arising from the use of the firearm, whether or not there was an independent felonious purpose to the use of the firearm, was an error of state law. Precedent holds that this should be examined for harmless error, seemingly establishing a Due Process violation by implication, but one not clearly established for the purposes of Habeas petitions. Here, though, the error of stare law was harmless, as the verdict would have been the same.
http://media.ca7.uscourts.gov/cgi-bin/rssExec.pl?Submit=Display&Path=Y2018/D09-21/C:17-1838:J:Griesbach:aut:T:fnOp:N:2222884:S:0
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.