I've seen it all now...

[Goober]

http://www.amazon.com/Archery-Tac-15-Crossbow-Upper-1135/dp/B001SGZG9K/ref=sr_1_59?ie=UTF8&qid=1351992406&sr=8-59&keywords=ar15+lower+receiver

http://t.qkme.me/3qnf8k.jpg

[2Kblacksleeper]

Yea it came out a year or two ago. Cool idea. Priced a little high.