With long guns,it's not the number you buy,I've bought 6 long guns in a day (Mauser/Winchesters)however,it's what you are doing with them?
If thought of "flipping" them comes to mind,then selling for profit will cause an Alert somewhere,sometime. ATF just got a guy in my town selling AK's out of this trunk and he's gone for 5 years..they were also trying to tie him with some smuggling charges,but I guess they didn't connect on that one and took the five in the big house...