Waiting periods for gun purchases may not make a difference, because "If somebody's decided that they're gonna take their life, they're gonna take their life."
Yes, waiting periods on gun purchases have been linked to suicide reduction [...] Proceedings of the National Academy of Sciences, "Handgun waiting periods reduce gun deaths," Nov. 14, 2017 CNN, "Handgun waiting period laws save lives, study says," Oct. 16, 2017