Do you want to mess with the BATFE? Like the $200 tax stamp? When you're finished, you still have a pistol with a fancy stock. Why? Get yourself an AR SBR. Then you'll have 2 cool guns! Pistol caliber carbines have fallen out of favor because, well they are still pistol calibers! I had a chance to shoot an HK MP7. That is what you really want. If you can get one do it. They are running $5K used right now. But the there are even more restrictions.