The unsupported chamber shouldn't be a problem with factory loaded ammo. The problem is when you try to reload brass shot from an unsupported chamber. Since there's no support in the bottom around the case head, you get a little bulge in the brass there which is affectionately known as the "Glock smile".
That bulge is a pain in the ass to get out when you resize the brass case, and it also weakens the brass more than it would be if shot from a chamber with full support.
On the other hand, that unsupported chamber also aids in the feeding reliability of ammo, which is one of the main reasons the Glocks have the unsupported chamber.
