The source is your calendar. Take a look at it. Today is July 22. Congress goes on its summer vacation from July 26 (read: Monday) through September 6 (again, a Monday).
The AWB expires on September 13 (yup, Monday). Now count the days, minus the weekends.
6 Full Legislative Days Left Until The AWB Expires
"6 Full Legislative Days Left Until The AWB Expires"
So, after Sept 13 does it take a different kind of vote than it would for an extension?
Since the import of certain foreign made weapons like AK47 are already banned anyway, how will this affect gun sales? Just make it easier to modify rifles with pistol-style grips, folding stock, etc made after a certain date?