I had the same problem on my old computer (haven't used Weapon yet on the new one). If you use just fire the rockets without changing the amount fired, you will fire 60 at once, which will overload your computer until they explode. However, if you change it so you are only firing four or less at a time, there should be no problem.

When you say that Weapon affects your performance, do you mean just in this instance, or with everything else? While I had this problem with rockets, missiles and guns worked perfectly fine.