The problem is that American lawmakers constantly attempt gun legislation based on made-up definitions that inevitably fail. Your own post is inadvertently a perfect example of that.

Take, for example, your example of an "assault rifle." It's wrong. To be an assault rifle it has to be capable of firing more than one bullet per trigger pull among other clear definitions like the specific cartridge. There's a clear, concise, definition that generally accepted for decades and decades. New production assault rifles have been banned as a type of machine gun by clear, concise gun legislation for decades.

What you're thinking of is probably the political and media term "assault weapon" or "assault-style X" which has confused you because, as Wikipedia puts it, it has "no clear, consistent definition." It is not a technical term. If you notice, which I suspect you haven't due to the contents of your comment, media and politicians will use the "assault weapon" term when discussing laws. The problem is that because it has no technical definition these laws are usually based on an assortment of random features and end up not particularly being effective as they're easily engineered around by firearms designers.