My Glock 19 and 26 have a circular recess cut into the front of the barrel lug which perfectly centers the guide rod when you're reassembling the slide/barrel/recoil spring package. The Shield design asks you to center a circular disc at the back end of the RSA on top of the circular barrel.
It really isn't THAT tough to do when you know what you're supposed to do and pay attention while doing it. But I have to wonder how hard it would have been for S&W to cut a Glock-type notch in the barrel lug, and make the correct alignment of the RSA automatic??
