Ok, let's throw a hypothetical out there. (I'm just playing Devil's Advocate.)
Two men walk up to a seller, and one of them says, " o, here is my ID, and I would like to purchase this gun for my friend. His name is Abdul Ja-quim, and he is a terrorist. He plans on using this gun to shoot a government official. How much will that gun cost?"
Now, there may not be a law on the books that specifically prohibits this, but I doubt the scenario presented above would make the sale of that firearm illegal.
What if we made it slightly more realistic, and the purchaser just said, " o, I'd like to purchase this gun for my friend, who is not allowed by law to purchase guns."? Would that be kosher?