Soft shackles work so well, many people are worried the noose will slip off the head, since that is the only thing keeping it in place. A standard button knot soft shackle has the legs completely separated until the noose but John Tucker wanted to try to test brummel splicing them together which, in theory, will keep it snug up around the knot.
He used Samson SK75 7/64 (2.5mm) 8 braid Dyneema. I pulled with the knot in different positions to see if we got the same results regardless. I pulled it with a hydraulic without any pretension until ultimate failure.
Does Bury Length Matter
A general rule is that you need 72x the diameter of dyneema spliced into itself to be full strength. Does this apply to soft shackles? John did a proper bury length of 8" with the last 1" tapered and then did some short burys and then on 1 set, he completely cut off the tails and it has 0 bury.
Does Knot Size Matter
The button knot is a bigger knot than the diamond knot and it also allows the tails to come back down so you can make the diameter below the knot larger for the noose to have a better bend radius, therefore getting consistently higher results than a diamond knot. Since John is worried about the noose slipping off, he experimented with putting an extra pass in the 3rd stage of tying the button knot so it would be bigger.
The knot didn't seem to have a difference, except it just makes it harder to tighten up which is an important part of making these. A longer bury has not proven to be important in my experience of using soft shackles (aggressively) for many years. A short bury is super good enough but as you can see with the heads getting decapitated, that you don't want to just cut the tails off. I've pulled on soft shackles with tails that were not buried in the past and it collapses the knot. The brummel splice technique for John's soft shackles did not seem to have any negative affect on the strength.
This is John Tucker's video on how he made the soft shackles you see in our episode.
We tested tapers to see how much they matter. If you don't taper you get a drastic change in diameter which in theory reduces the strength, but we actually found out something even more interesting trying to discover that.