There is zero chance he has the wrong bushing if the barrel is able to be installed. The Shadow barrel is 0.550 inch, the standard barrel is 0.500 inch.
It's tough to tell by the pictures but is the bushing fully installed? It looks like it may not be flush with the muzzle end of the slide? If that bushing is not colinear with the barrel it may not allow it to move. It needs to be flush with the end of the slide to ensure it is colinear with the barrel
I'd second measuring the bushing diameter and the barrel diameter. If you can't insert the barrel backwards into the bushing, then something is out of spec.
Cheers,
Toby