That shot isn´t that long.
It takes a little practice but this is a way it works:

Take the shell between index finger and middle finger. It should be close to the knuckles. The open end is about even with the back of the fingers. It must have a slight downward angle with the back of the fingers. The proper position is about half the distance between the knuckles and the first joint (you´ll have to experiment a little). Now make a fist and put the first joints of the fingers holding the shell to your lips. When you blow you can vary the angle untill you get a loud shrieking noise. It works with about every shell you can hold properly.

BTW:
Way back when I was a child we used to employ the caps of acorns for that (mommy couldn´t sucessfully confiscate those). That proves once again that playing is practicing surval skills <img src="images/graemlins/laugh.gif" alt="" />.

When you wish to convert the shell you have to dent the shell before cutting it open. That way the lip is in the air flow. The noise is lower than with the above method though. For this a .22 magnum shell is better than the .22 lr and it´s still smaller than the 5.56 mm.