I'm sure you figured it out by now, but in case you didn't....

your user control needs to have properties exposing its controls.

In your user control class add following property:

Code:
        public DataGridView InnerDataGrid
        {
            get
            {
                return dataGridView1;  //This should be the name of your DGV
            }
        }
Now, in design time ,you'll see the property "InnerDataGrid"