Hi there fellow rock-chuckers.
 
I recently stumbled across your neat little corner of the web here and have really been enjoying reading about slinging.
 
As someone who is slightly impulsive, I ran out and bought a spool of jute string and promptly built a "Rockman" style sling.  The next time the family and I went out to the river, I trying slinging a few rocks.  
 
Two things became immediately obvious.  Throwing rocks is fun, and slinging is a lot harder than it looks.
 
I've watched a really great video on how to do the figure-8 style of throw (can't remember the fellow's name right now) but for some reason I just wasn't getting very much distance on my throws.  
 
It felt like the rocks I was using were too small for the sling.  I expected to feel more centrifugal force when using the sling than I did.  The sling almost felt "empty" for lack of a better term.
 
A tennis ball might be a better size/weight object for this sling.
 
Next on my list is a leather-pouch sling using some low-stretch dyneema rope I have left over from my hammocks.
 
I look forward to "meeting" you all here and learning how to really get some rocks flying.
 
Mike

don't sweat the lack of distance.  
the fig 8 video was probably brian grubs.  
 
The biggest mistake beginners make is trying too hard. You have to learn to let the sling do the work, a smooth relaxed style will usually get your rock further than one you try and muscle.  
 
So next time, try and relax. Throw slower and let the sling do the work. you should find it becomes alot easier and your distances increase dramatically

Welcome Mike. Good to have another West Coast member. No doubt if you keep slinging you will find that wherever you go your eyes are glued to the ground looking for perfect stones. I think some parts of Oregon have really good areas for sling stones though? Looking forward to seeing your sling.

Hi, Mike;
   Welcome.  That Brian Grubbs video is one of the best slinging instructional videos I've ever seen.  David Morningstar has some very good ones also, as do others.  We would love to see a picture of your Rockman.