You always hear rocketeers complaining about shock cords for one reason or another. The main bit of advise which you hear time and time again is: 'Don't use the shock cord that came with the kit'. The main reason for this being that many manufacturers provide either a short or weak shock cord with the kit. Some manufacturers are better than others.

The shock cord it's self should be fairly long, fairly thick/wide and be able to withstand the occational bit of scorching. It doesn't have to be elastic - it just needs to be long enough (2 or 3 times the length of the airframe) to allow the nose cone time to loose kinetic energy (slow down) so that it doesn't 'grab' the rocket. Tubular nylon is a common choice with many rocketeers flying larger rockets.

Tips from the rec.model.rockets FAQ:

6.11 Improving on the Estes Shock Cord Mount

There are a number of ways to improve on the old paper-and-rubber-band shock cord mount used by Estes for the past 35 or so years. The following suggestions have been repeatedly made in r.m.r.

1. Replace the rubber band or short elastic in the kit with sewing elastic at least twice the length of the model. This will help to avoid tube zippering or ripped out shock cord mounts when you have a 'hard' ejection.

2. Epoxy the shock cord mount to the inside of the body tube rather than using white or yellow glue. Thirty minute epoxy works best for this. Be sure and lightly sand the inside of the tube where the shock cord mount is to be placed. Also be sure and 'cover' the entire mount with a very thin layer of epoxy. This method works best for models with BT-60 or larger body tubes.

3. Use a 'Quest-style' kevlar-and-elastic shock cord mount. This type of mount uses a length of 50 to 150 pound test Kevlar (such as Stren Kevlar fishing line or Kevlar kite string). The Kevlar is tied and glued to the motor mount (motor block, centering ring, or around the motor tube). It is sized to end just shy of the front end of the body tube when a length of elastic shock cord is tied onto the free end of the Kevlar. This method eliminates any shock cord mount on the inside surface of the body tube. Estes-style shock cord mounts have been known to interfere with parachute deployment. You can used this method on any sized rocket. Size the Kevlar appropriately.

4. You can also use a 'LOC-style' shock mount for body tubes in the 1.5" and up range. With this you take a short length of Kevlar line, fold it in half, and make a 1-2" loop in the closed end of the folded line. You then epoxy the loop to the inside of the body tube in such a manner as to have the end of the loop extend a little past the open end of the body tube. A shock cord is tied to the loop. The advantage of this technique is that is allows damaged shock cords to be easily replaced. It tends to work better on body tubes greater than 1.5" in diameter.