How Do I Get a Glyph's Bounding Box After a "glyphshow"?

I am trying to capture the bounding box from painting a character using glyphshow, but the result seems not to be the actual bounding box.  Here is a snippet of PS code that I am trying:

% begin snippet

/BickhamScriptPro-Bold 70 selectfont

0 0 moveto

newpath

/glyphname glyphshow pathbbox

/ury exch def

/urx exch def

/lly exch def

/llx exch dev

% end snippet

I use the result to center the glyph like so:

% begin snippet

/hw llx urx add .5 mul def

0 hw sub 0 moveto /glyphname glyphshow

% end snippet

For the glyph I'm using the result is not centered ("d.begin", font: Adobe Bickham Script Bold).  Note the glyph is a very slanted cursive 'd' with the upper right part extending well over adjacent characters to its right.

What am I doing wrong?

Thanks.