You have a S&W screw up. Someone got a 9mm barrel into the box of 40's and you ended up with the wrong barrel. But lucky you, as you can contact S&W and tell them of the problem. They will likely ask you to send the gun back. Explain this is your only carry gun and you don't want to be with out it. You can send them pictures of your slide and barrel and ask for the correct barrel be sent to you. Tell them it is not your fault someone at their assembly department screwed up.

If all works right, you might end up with what all us 40 owners want, two barrels (the stock 40 plus a 9mm). Then you have a gun with the best of both worlds, a 40 for high power SD, and a 9mm for less practice recoil and cheaper practice ammo. Don't forget you still have to practice some with the 40, so you know what to expect in recoil and time needed for target re-attainment.

Keep us posted on your outcome with S&W.

Bob