what is the weak point on a sling

This is kind of a random question and I guess it really doesnt matter, but I need to satiate my curiosity. When a sling gives a rating of 22kn or whatever it may be, what is the weakest point on the sling? is it the sling material itself (dyneema, nylon, etc) or is it the stitched point that connects the two ends together?

I also have a question about water knots. Would a water knot be sufficient to use in a back up or emergency situation to make a sling. If a fall was taken on the sling would the water knot cut through itself under pressure. It seems that the dyneema would cut through itself easier because it is so much smaller in width, but Im not sure.

Thanks for reading this, Ive just had a few things running through my head and thought I would pick your brains.

Cody

The weak point on a sling is where it lies over the karabiner, that´s where they break (in testing this is a 10mm diameter steel pin).
With Dyneema tied with a water knot normally the knot fails as the sling slips through.

In most cases the weakest point on a sling is the user ;)

Water knots, of course, work fine with standard nylon webbing to make slings (old school bonus points). Water knots are not appropriate for dyneema or spectra for a couple of reasons. Mostly the material doesn't generate enough friction for the knot to hold so it pulls out. yikes. dyneema and spectra should only be sewn, never tied. ...double fishermans will work in fatter spectra but I just stick to the idea of "should only be sewn".

Great video on the subject on dmm's site dynex spectra and other non nylon sling materials actually melt apart under a dynamic fall when knotted. As for regular nylon fall away. water knots are great for making some of your own slings... you can even use a beer knot if you want a lower profile for the knot.