Challenging A Coroner

Is there a way without using a lawyer to challenge a cause of death finding from the county coroner. Basically my Dad died New Year’s Eve from a self inflicted gunshots. He first accidentally shot himself in the leg while fumbling his .38 trying to answer the door to a loud noise coming from the porch. Then asked my mom to call 911 and to get him some clean sweatpants and underware so he could got to the hospital. While my mom was retrieving the things he asked for she heard a second shot and came back to find him dead on the floor. The coroner listed the cause of a death a suicide which there is no way this man committed suicide. I know my dad and his stance on gun rights and gun saftey and it just isn’t in him to do that to himself and our family. What should I do to challenge this it is going to make my mom and his life insurance an issue and it’s just not right