After getting shot by Thornton, Lukes goes after him, but leaves his gun. On the ride to get Thornton, Luke still has no gun. But when doc brings him to town Luke has his gun on when being helped off the buggy.
The synopsis is used with permission from the person who e-mailed me. These are his own words & not copied.
Robert Lansing actually says the word "Gunsmoke" in this episode.