Problems Using Copymovieclip

i want to make a copy of my movie clip 3 times in a row.
but when i copy them its only one of the copies which are shown, why?
i used
mc1.copymovieclip("mc2");
mc2._y=mc2._y+50;
mc2.copymovieclip("mc3");
mc3._y=mc3._y+50;
mc3.copymovieclip("mc4");
mc4._y=mc4._y+50;

but its only mc4 and mc1 (which is the original one) that is shown.
-Hashmus-