Seems like everyone on this post is talking about loops on the end of the fly line.
You asked about a loop for a hand tied leader.
I assume you mean for a loop to loop connection for quick changing tippets.
The perfection loop can slip. You are better off tying two Kreh non-slip loops.
See: [url=http://www.flyfisherman.com/skills/lkknots/index1.html:be4bc]http://www.flyfisherman.com/skills/lkknots/index1.html[/url:be4bc]

When you connect the two loops it helps to form a Harro cross in the connection as it will prevent a girth hitch.
See: [url=http://i5.photobucket.com/albums/y151/DickM/Loop-To-Loop-Connection.jpg:be4bc]http://i5.photobucket.com/albums/y151/DickM/Loop-To-Loop-Connection.jpg[/url:be4bc]

[This message has been edited by DickM (edited 28 May 2005).]