Doc said:
I start with a long piece and tie the first knot and then tug and pull on the remaining loop material to get the first knot as tight as I can. This also removes some of the "stretch" in the material. I then tie the second knot so the loop is much smaller than I need. I place a pair of needle nose pliers in the loop and open them up. This helps to produce a d-loop with minimal stretch for me.
Doc's method is right on.
I am having good luck with pre-strectched loop material. Of course, proper loop tying is critical.
I have tested several different loop materials. I have found that most loop material experiences a noteable amount of stretch under static weight. I have measured the stretch to be about 1.5 inches on an 90 inch lentgh of material. Some more, some less. But, all materials stretched.
What I am doing is waxing the loop material well. Then, I am hanging 65 pounds of weights to the end of a 90 inch length of material. Most of the stretch occurs within 8 hours.
All that said.... If you pre-stretch your, well waxed, loop material you will likely decrease the amount of loop stretch. Your knots will cinch tighter.This is due to the diameter of the loop material being decreased as it is strectched, and the added wax.
I hope that helps some,
Bambi Killer