YHM 5.5" barrel Class 3 only?

[Ub3rD0rk]

I went onto Yankee Hill Machines wesite to order a 5.5" 9mm barrel for an AR pistol I have and the website says it can only be ordered by a dealer with a class 3 license. I stopped in at Ammo Bros to see if they could order it for me and there order program says the same thing. The guy at Ammo Bros is going to give YHM a call tomorrow to see why they require a class 3 for just a barrel. Anyone else have any idea why this would be?

http://yhm.net/index.php?main_page=product_info&products_id=476