Bill,

Apparently Excel does not set the chart autoscaling to false before saving
the chart as user-defined.  As a result, the chart font sizes appear to
change when the chart is saved to the file that holds the user-defined charts.

To prevent this from happening, activate the chart that you want to save as
user-defined by clicking on it.  Then, run the following macro.  

Sub DisableAutoScale()
   Application.ActiveChart.ChartArea.AutoScaleFont = False
   MsgBox "AutoScale Disabled"
End Sub

The macro will freeze the font sizes.  Now, save the chart as user-defined.  
The next time the chart is used, it should appear as it did when saved as
user-defined.

Alternatively, you can download a copy copy of John Walkenbach's Chart Tools
add-in.  The add-in includes an option to freeze the text size of a chart.  
It is available at http://www.j-walk.com/ss.

----
Regards,
John Mansfield
http://www.pdbook.com