Here’s a unique upper for your AR-15, Tac-15 builds crossbow uppers that attach right onto your AR-15 lower. While it’s not new, I recently stumbled upon it while researching for a new AR upper. Tac-15 claims their crossbow uppers are the most accurate and powerful crossbow on the market. They currently have four models available, check them out at Tac15.com.
Another toy I want for my AR!
The problem is you are still legally carrying a RIFLE. Serial numbered receiver. There are areas where this would get you jailed.