There are, of course, arguments to be made for either side of this question. I will briefly outline an argument for each side and you can decide which argument you prefer.
On the one hand, we can say that gun manufacturers should not be allowed to advertise. Their product is one that is used to kill huge numbers of people every year. Since their product is so dangerous, it is not something that should be advertised. We should prevent such advertising so that not so many people would want to have guns and the amount of gun violence in our country would decline.
On the other hand, we can say that such ads absolutely must be allowed. First, under current legal doctrine, the right to own a gun is protected by the Constitution. It would be very odd to prevent manufacturers from advertising a product that is specifically protected by our founding document. Second, people can have many reasons to own guns other than killing people. A person might want a gun simply for target practice. A person might want a gun for hunting. A person might want a gun so they can scare away someone who might be trying to harm them, even if they do not kill that person. Gun manufacturers, then, are selling a product that has a variety of uses and one which is protected by the Constitution. Given this, it is unreasonable to ban advertisements for this product.
Which of these arguments makes more sense to you?