Outlook adds an extra 6px or so to each table. What you have to do is trick Outlook into thinking they are table cells rather than stand alone tables. If they are already wrapped in another table all you have to do as add
<!–[if gte mso 9]></td><td> <![endif]–>
in between each table.
I wrote a bit more here about that:
You could use:
See more here:
edit: Actually, I'm not sure that will work out of the box, you have to set encoding on your subject line.
Depending on your design you can set your responsive table to 100% at your break point and it will then fill what ever the device's width is.