I was working with a client the other day creating column charts of data where the horizontal axis was made up of dates. We wanted to make the columns wider, but trying to format the data series to change the width was not possible.
The trick needed is to format the axis as text.
Click on the horizontal axis, right-click and select Format Axis. On the Axis Options tab, in the Axis Type section choose Text axis. Click Close. Your columns become wider!!!
You can then further adapt the widths by right-clicking on the column and selecting Format Data Series.
The smaller you make the gap, the wider the columns become.