Straw purchase really has nothing to do with whether or not the actual end recipient can legally own a firearm, but more with the intent. If you ask your brother to purchase a firearm for you, then yes, it would be considered a straw purchase under the law. If your brother decides on his own to buy a rifle for you as a gift, then it is not a straw purchase. A fine line, but it is there.
Of course, this assumes all other laws are followed - i.e., there are no state laws precluding this and you are both residents of the same state. In your case, you are not, so the point is somewhat moot. The transfer needs to go through a licensee in any case.
Taken from the 4473:
1. For purposes of this form, you are the actual buyer if you are purchasing the firearm for yourself or otherwise acquiring the firearm for yourself (for example, redeeming the firearm from pawn/retrieving it from consignment). You are also the actual buyer if you are aquiring the firearm as a legitimate gift for a third party. ACTUAL BUYER EXAMPLES: Mr. Smith asks Mr. Jones to purchase a firearm for Mr. Smith. Mr. Smith gives Mr. Jones the money for the firearm. Mr. Jones is NOT the actual buyer of the firearm and must answer "no" to question 12a. The licensee may not transfer the firearm to Mr. Jones. However, if Mr. Brown goes to buy a firearm with his own money to give to Mr. Black as a present, Mr. Brown is the actual buyer of the firearm and should answer "yes" to question 12a.
As mentioned though, this all goes out the window for interstate transactions.
Rocko