I built the Big Daddy exactly according to the Estes instructions, using the supplied parts.
Steven, I was thinking about this again, and the reports by some of these other guys about deployed chutes not opening well, and I started wondering about your shock cord length. I guess great minds think alike?
The first thing I would do is toss the Estes shock cord. My apologies to Penrose, but the provided cords are just too short.
You need one that is significantly longer---some guys here on TRF recommend using a shock cord that is three times the rocket's length (for low-power rockets). I suppose it wouldn't hurt to use four, or five times the length, but you begin to get different deployment problems where the shock cord stays in a bundle and pulls into a tight wad (instead of spreading out to full length) after ejection. Maybe there are tricks to attaining a "tidy" and complete extension of the full length of the shock cord, like maybe some secret techniques used by parachute packers?
Anyway, a short shock cord (as is often provided for many kits) runs the risk of having the NC pull the shock cord out to full extension (after ejection) and then snapping back to whack (and dent) the rocket. In fact, the "Estes dent" is a fairly famous type of damage that many people have had happen because of short shock cords, and it is soooo easy to avoid.
And, with stubby rockets, a parachute held close to the rocket easily not get much "clean" air to help with full opening of the chute.
I like to use a strong heat-resistant cord that anchors to the rocket and reaches six to twelve inches (or longer) outside the rocket. This is the main tether part that is exposed to the hot ejection gas. I use Kevlar if I have it available. I have also used heavy cotton and nylon cord but soak and coat those materials with white or yellow glue to improve their resistance to flash flames. I look for a tether with enough tensile strength to stand up to 20 pounds or so of pull, more if my low-power rocket is a big & heavy one.
I tie the end of the main tether in a small loop at the loose end. This lets me tie on any additional length of non-stretching tether that I might want to use, or I can tied on some stretchable elastic band to absorb some of the "shock" of the NC yanking on the other end of the line. I use a length of stretchable shock cord that is about as long as the rocket, maybe longer. The material is the 1/4 inch wide elastic band that comes in six foot lengths for around a buck; you can find it in the sewing department of many stores. (They also sell wider elastic band material that you can use for heavier rockets.) This arrangement lets you pack the stretchable part of the shock cord up ahead of the ejection wadding and keeps it away from the hot ejection gas.
Some folks like the stretchy "rubber band"-type material that comes with many kits. That's fine, I just recommend that you keep a close watch on the stuff. I have found that once this rubbery material develops a nick on one edge, it can easily tear all the way through the entire width. It seems to toughen and dry out after long storage, or after many ejections, faster than the elastic-band material (IMHO).
For low-power rockets, I don't like making the entire length of the shock cord from non-stretchable material. I like to have roughly half-n-half up to where the parachute (or streamer) attaches, and maybe even another short piece of tether material on out to the NC.
All parts of the shock cord system (anchors, tethers, stretchable cord, knots, swivels, clips, etc.), regardless of materials used, need to be inspected frequently and repaired when you see damage (fraying, roasting, stiffening, etc).
As far as guidelines on how long to make the whole shock cord (for low power rockets), as far as I can see, the "three times the length of the rocket" rule of thumb seems to work. You would probably be OK at two times, or four times, but it's not all that important. What
is important is to watch out for shorty cords provided with many kits--and replace them!
Sorry if this response was overkill, but I wasn't sure what sort of answer you needed. I hope some part of all that is useful to you