Thanks kitefisher. The loop length is not important, 50mm allows me to put a finger through the loop, which in turn helps apply tension during the process.
Bobbin is perfect, the knot is after all a modified pr knot. The nice thing about a sinker is that there is always one available, even on the rocks. It works for braid to mono as well, and even then after 70/100 turns I go between the lines. You will notice that this becomes almost a transition point. Especially thinner leaders, you will see the leader starts turning over the braid, and the braid remains more or less straight.
This method can be used to make loops as well. You also don't have to use one length of braid. You can for eg use 30 lbs braid to do the wraps around 50 lbs braid. Instead of the uni ending with a loop you just tie back to back unis. Just do the turns in the opposite direction to the turns in the unis. You can even use it as a crimp. 10 oz sinker, 1mm line works for 400lbs cable. Obviously not made of steel so a crimp as backup.