I created a bootstrap grid views block with 4 columns. When I visit the page in mobile device, I see one column grid. When I visit the page in tablet device, I also see one column grid plus blank to the right.
What classes exactly did you use ?
The breakpoints used for the grid could be different depending of what device size you aim for your columns.
The smallest size handled by the BS grid is for devices with < 768px width by adding class
col-xs-* (in Boostrap 3, for Bootstrap 4 it's up to 576px).
Typically this is for some tablets & almost all smartphones in portrait mode.
If you only want set classes for superior size, it will automatically be stacked on extra small devices.
For example, if you used
col-md-3 for each column, when the device width will worth < 768px, all the columns will be stacked each under the others (which is often wanted on small width regarding layouts).
But you can add
col-xs-6 too on each to have 50/50 columns on small devices.
See more Bootstrap documentation about the Bootstrap grid system : http://getbootstrap.com/css/#grid-options