I make and use 50# double-locked braided mono loops, but I fly fish saltwater with shooting heads almost exclusively. The 50# braided mono gives me a connection stronger than the core of any line or head...important when you consider the forces in play at the loop when casting heavy shooting heads for distance. Heres two excellent articles on how to make them:

Dan Blanton's "Getting Looped" Article:
http://www.danblanton.com/gettinglooped.htm

Mike Figliori's Step-by-Step Directions:
http://www.flyfishsaltwaters.com/building_braided_loops.htm