Denis9834 posted about some problems he had right out of the box with his new M&P 15:

M&P 15 sport 2 jamming and bending rounds

His post suggests that I should do a break-in period. How many rounds should I fire when I pick up my new M&P 15 to confirm that it's reliable?

I just realized that the LGS didn't show the actual rifle to me when I filled out the paperwork for background check and payment. I'm new to AR-15s, but I know enough to confirm the serial number. I'm wondering what sort of inspection I should do in the store before I take it home?