While you are on the site, in your browser find and click "Add to Home Screen" A CGN beaver app icon will then be created to your phone that is directly link to the site.
Note: This feature may not be available in some browsers.
Perfectly normal. Have you field stripped the gun yet to see how little is holding the barrel in place when the slide is back? Quick answer is "precious little".
When the slide is forward into battery there are ridges or other features on the barrel that lock into matching mirror images that lock the slide and barrel together. There should be very little or no rattle of the barrel when the slide is in battery.
Why are you shaking your gun? As BC said it's completely normal, but definitely make sure it's solid when the slides closed. You'll know pretty quick when shooting it if there's a serious problem, it will shoot patterns instead of groups.