There are so many laws on the books that there is no lawyer alive that knows it all. Old laws rarely go away, they just do not get enforced any more. Its almost impossible to live day to day without breaking some law, that we never knew existed.
Aditionally most laws, esp.firearms laws are writtem by people, lawyers, that have little to no understanding of firearms whatsoever.
Additionally firearms laws are meant not to punish someone for "wrongdoing" against society but to keep people under the thumb of government. I believe they are intentially written to be confusing and trip us up. Its rarely the common criminal that gets caught in the mire of legalities but the common man who is trying to do the right thing and still gets caught in the web.
How is any gun law not, by definition, an infringement?
How many of them reduce crime? Keep us safer?
Yet people continually support these laws under the false promise of being safer, protecting their children, etc.
Guns don't kill, or hurt people. They are just pieces of metal and plastic. Evil, sick and angry people kill other people. They have been doing it since the dawn of man without guns and will continue to do it until the end of man with whatever objects they can find. The best defense for this are armed good guys.
/rant
Back to the topic. It should not matter what stock, foregrip, length of barrel, magazine, barrel shroud, suppressor, etc. one affixes to their firearm. Non of those things change the inherent mature of that chunk of metal. All it does is change its appearance.