Wide table, horizontal scrolling

I have a fairly wide table, and am trying to get it to scroll horizontally. Has about 15-30 columns.

The rendered div dataTables_scrollBody has a width of 1161px, I assume calculated. The table has a width added too.
In firefox in the inspector, if I change it to 100% it behaves better. I am not sure what I do to trigger the numerical width.

I see in the code something about iSanityWidth, might be that.
I tried various values for sScrollXInner, to see if it helps.

var oTable = $('#Fuzzy').dataTable({
"bFilter": false,
"bSort": false,
"bInfo": false,
"sScrollX": "100%",
"sScrollY": "400px",
//"sScrollXInner": "2000%",
"bPaginate": false,
"bScrollCollapse": true

});
var oFC = new FixedColumns( oTable );

Any help appreciated.