Macro terminates prematurely

Hi Forum Friends
I have a macro to reset certain column that are offset by 13 to the right.
If the test for the loop is ActiveCell = BLANK the macro works, but creates an
un needed column at the end.
If I test for a Blank cell before copying the formula the macro ends prematurely.
I am stumped.

Sub BClear()
    x = 0
    y = 0
    If Left(Range("L38"), 3) = "M-X" Then
        y = 8
    Else
        y = 13
    End If
    Range("F54:F100").Activate
    Selection.Copy
    Range("F54:F100").Offset(0, 10).Activate
    ActiveSheet.Paste
    Range("F40:F230").Activate
    Selection.Copy
    Do
        x = x + y
        Range("F40:F100").Offset(0, 10 + x).Activate
       ' ActiveCell.Offset(1, 0).Activate
        ActiveSheet.Paste
    Loop Until ActiveCell = BLANK          'works, but creates un-wanted column
    Loop Until ActiveCell.Offset(0, 10 + x + y) = BLANK   ' stops on column 107
    Stop
End Sub

Merry Christmas
Al