According to the BATFs Annual Firearms Production and Export Report for 2011 S&W produced in 2011:
736 Misc. firearms and 14 shotguns
From the Houlton plant they produced 56,527 pistols.
If we look just at the revolvers S&W produced in 2011 they produced more than 650 in a single day if they worked every day of the year, which we know they didn't.
Ruger produced 610,925 pistols for the year 2011 and 193,025 revolvers.
Colt 46,363 pistols and 1454 revolvers.
So if the math is done we can see that in 2011 S&W produced far more than 300 handguns a day despite the "union rules" holding them back.
The complete report can be found here and it reports on all firearms manufactured in the U.S.
Scroll down and find the manufacturing and export reports for each year they have available.
So one thing we learn is to not always believe what gun store clerks tell you till you check the facts.