Some individuals have always had the ability to make modifications, but that has nothing to do with what is legal and available over the counter. An illegally modified machine gun will still be an illegally modified machine gun. Banning the manufacture and sales of machine guns, as if they were any other gun was done for one reason, and one reason only. Their rate of fire was too high. Laws concentrating on how they were designed seemed like a good way to reduce the number of high firing guns on the street at the time, In time it proved to not solve the initial problem of an extremely high firing rate. If we ban bump stocks, someone will design something else that will do the same thing, only better. That's why we should do what should we didn't know to do from the start. Ban guns with the ability to rapid fire. Manufacturers can come up with any design they want, as long as it meets other applicable standards, and is not capable of exceptionally high firing rate. Yes, some people will still be able to illegally modify them just like they can now, I have no idea how they might limit the firing rate, but I also have no doubt that someone will know. When a gun is found with it's rate limiting ability bypassed, it would be the same as when they find a gun with an illegal DIAS now.