When you set width to a RadDock, the actual available space for content is less than this width, because the dock's borders take up some space. This may be unexpected by some people, but otherwise the dock itself will take up more space than specified, because the borders would add up to the dock's width.
In addition, RadGrid by default has borders for its wrapper <div>. No matter what the RadGrid width is, these borders add up to the width and depending on the layout, scrollbars may appear - this is normal and is according to the W3C CSS specification.
So you have two options:
1) Remove the RadGrid borders and set Width for RadGrid, which is equal to the RadDock width minus the left and right dock border widths, e.g. 305 - (1 + 1).
2) Leave the RadGrid borders and set Width, which is equal to the RadDock width minus the left and right dock border widths and minus the RadGrid left and right border widths, e.g. 305 - (1 + 1) - (1 + 1).
By the way, I don't see why you need that <div>, you can set a pixel width directly to RadGrid.
Let us know if you need more information.
the Telerik team