Ok, so for Bar Column usage is mandatory to set manually the Axis Plot Properties.
But this create a lot of problems.
Please look my other post in http://www.telerik.com/community/forums/wpf/chart/datetimecontinuousaxis-ticks.aspx#2695711
I have attached a project that shows another approach - BarSeries with PointTemplate with data-bound Width property. This allows you modify the bar width directly when needed (eg. when the ZoomChanged event occurs). Additionally, you may find useful the RadCartesianChart.PlotAreaClip.Width property, which you can use to get the available plot area space.
I hope this helps.
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