I don't think it is so easy, especially if you are rigorous about your criteria and reasoning.
Double-effect has four criteria for making a judgment in any particular case. The intent of the maker is only one of the four. The most pertinent criteria in the case of the hunting rifle and school shooting scenario is the last, of proportionality. Does the good to be gained by having hunting rifles exceed the evil to be suffered by school shootings?
That's a tougher question to answer than whether there is an ill intent.
Not tough. The answer to that particular question is "yes". The number of lives saved using rifles far exceeds the number taken without just cause. And when it comes to defending my family, "proportionality" is irrelevant: statistics mean nothing when they happen to you. Careful how you apply your reasoning, lest every right you cherish be denied you in kind.
Double-effect has four criteria for making a judgment in any particular case. The intent of the maker is only one of the four. The most pertinent criteria in the case of the hunting rifle and school shooting scenario is the last, of proportionality. Does the good to be gained by having hunting rifles exceed the evil to be suffered by school shootings?
That's a tougher question to answer than whether there is an ill intent.