December 2nd, 2016, 10:17 PM
Join Date: Jul 2004
Location: Cincinnati, OH
Verify first that the receiver is seated all the way down. Is the underside of the heel touching the stock, and also are the trigger pads touching.
I would also insert the trigger group into the receiver without a stock present, and just make sure that locks up as well.
It might just be a tight stock, but it would suck if you broke a trigger guard because it was some other issue.