Let me talk about strawman purchases for a minute. First off, I am neither a FFL nor a lawyer.
I have seen a gun going for an incredible bargin at a pawn shop. Guy didn't know what he had. I bought it. Two months later I sold it. The person I sold it to happened to have the handy little MN 'permit to purchase handgun/assault type rifle' so I know he was above board. This, provided I don't do it enough to need a FFL, is totally legal. In the above example, it was a 2 month window. To my knowledge, there is no required waiting period between purchase and resale.
I've also know a guy who was hot for pre 64 winchesters, especially ones from the mid 50's. If I happen to stumble upon one priced cheaply enough, I may well buy it, he has got a winchester model 52 I think is sweet as all hell, the 64 would be good 'trade bait'. I don't see anythign wrong with that, as we would each make private sales to eachother for each gun, all applicable laws for private sales will be followed.
I must note that in both of these cases, I have not received any money beforehand, nor any sort of ironclad contract. If my friend has to buy a new furnace for his house, he may well not want to buy the pre 64 off of me, he doesn't have the spare cash. That's okay, I'll try to buy his model 52 .22LR and still be happy, selling off the pre 64 someday, or maybe not, maybe keep it myself.
I've called a FFL to price check transfer fees for gunbroker type stuff. He asked what I was buying, because he wanted a chance to undercut his website competition (two basement FFLers, probably can get the same type of makarov or somesuch, hence he could charge me the same price as the posting, i save shipping and transfer fee, he gets sale)
Now, you can also buy a handgun through a FFL and give it as a gift. Legal, except it is my understanding that if you gift a firearm to a felon who cannot legally possess firearms that is still going to be viewed as a straw purchase.
It seems to me when you fill out the forms for transfer or purchase, you don't say you are purchasing the firearm yourself FOREVER. I don't know of any law that gives me a period of time I must keep the gun before I can legally sell it. Now I, as the owner, can choose to sell it. Then all state and federal laws kick in, regardless of weather it was owned 5 days or 5 years.
Seems to me his uncle did the same thing. Made a legal sale of a firearm he had in his personal collection. As long as the poster didn't give uncle the money beforehand. Now if it turns out that the recipeint could not legally own the gun, because he is a felon, crazy, illegal alien, or whatever, all those laws still apply, regardless of how long the uncle had gun in his collection before he sold it.
edit. I now see that you 'purchased' ammunition from him at a huge cost beforehand. This is what is going to get you into trouble.