Two firearms at once or two firearms in one week from your FFL. If the BATFE Agents come to talk to you they will know every Date, Time, Location of these transactions because they were reported on another form.
https://www.atf.gov/firearms/qa/mus...re-pistols-or-revolvers-are-sold-or-otherwise
And there is one for certain rifles as well.
Ah. So there could be a legitimate reason for the ATF to contact a buyer after a large purchase. But if they call you for that, you are the target of their investigation. How long after the purchase in bulk could you expect the call? The OP didn't indicate he purchased in bulk and he mentioned the call was a few years after the purchases.