WPF XAML ListBox bind to array

So i have a float array which i want to have as ItemSource in a ListBox.
Inside the ItemTemplate i have a progress bar, that should bind its Progress value to the given float value. Yet i can't ever see that the values are actually bound to the Progress property.

The xaml code (i don't know whether i'm wrong but i expected that there's a implicit cast from float to double):

<ListBox ItemsSource="{Binding CoreLoads, Mode=OneWay}" BorderThickness="0">
    <ListBox.ItemsPanel>
        <ItemsPanelTemplate>
            <StackPanel Orientation="Horizontal"/>
        </ItemsPanelTemplate>
    </ListBox.ItemsPanel>
    <ListBox.ItemTemplate>
        <DataTemplate DataType="{x:Type sys:Double}">
            <StackPanel>
                <ctrl:MetroProgressBar Orientation="Vertical" Progress="{Binding}" ExtenedBorderWidth="0.2" Width="30" Height="50" VerticalAlignment="Center"
                                       HorizontalAlignment="Center" BorderBrush="Black" BorderThickness="2" Background="White" Margin="5"/>
                <TextBlock Margin="0,3,0,3" HorizontalAlignment="Center" Text="{Binding LastUpdateTime, StringFormat='{}{0:hh:mm:ss tt}', Mode=OneWay}"
                           DataContext="{Binding DataContext, RelativeSource={RelativeSource AncestorType=UserControl}}"/>
            </StackPanel>
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

xmlns:sys="clr-namespace:System;assembly=mscorlib"

and the property itself:

public float[] CoreLoads
{
    get { return cpuManagement.ProcessorInfo.LoadPercentages; }
}