Very easy question to answer. The answer is "no". There was no ill intent, no expectation of misuse, no "mens rea" ("guilty mind"). The intended and expected market is very large and overwhelmingly upstanding. The good done far outweighs the freakish non-sequitur bad. You don't not do something just because, with a twisted line of reasoning, someone can conceive of 1 in orders of magnitude of orders of magnitude chance it might be abused.
Someone driving a car into a crowd does not make it Ford's fault. Society does not ban cars just because 50,000 people a year are killed by them.
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.
Someone driving a car into a crowd does not make it Ford's fault. Society does not ban cars just because 50,000 people a year are killed by them.