I have always used the braided stuff (300lb from Apogee) for anything D motor and above, even though it is overkill from a breaking force point of view. I think the skinny stuff is likely to floss the body tube easier during a sub-optimal deployment, so I go with the 1/8" or thereabouts braided. YMMV.
Ever so true about zippering. I flew a Fliskits Starlord last weekend for the first time since it was built over 7 years ago.
https://www.fliskits.com/products/01prod_fs.htm Back then I did a flawless paint job to look like the rocket on the insert.
I used some small diameter kevlar for a shockcord that could zipper the tube like heck if less than nominal deployment. I was going to get some RDF experience with a Beeline RDF tracker even though the flight was simmed to 1900 to 2000 feet and
I expected it to come down in sight using three E9-8's. Simmed the daylights out of it and 8 seconds is what it said was reasonable. I then had a flash idea to use a Jolly Logic Chute release with the logic that if the apogee deployment was a bit more early or late than I expected, the restrained parachute pack with the JLCR would be less likely to zipper the tube.
Well, my battery went bad in the tracker. I should have cycled/tested it as it was very old. Left it in the rocket as it was simmed with its mass. Launched it and it looked like it really got up there on the three lit motors. Apogee deployment
looked good and with the 8 second delay it seemed to have a very nice, slow ascent. Could barely see the rocket in the early stage of the descent but I did a very shiny clear coat over the color coat and could follow the flashes till it got lower.
I had the chute release set for 800' so I could get some hang time for using the (defunct) RDF tracker and the release did its thing right on schedule. Took a fairly long walk out to get it and when I picked up the rocket, there wasn't a single ding
in the cardboard from the kevlar cord. I did use a relatively long cord but it had tangled and didn't extend its full length. Nonetheless, the rocket had a nice first flight.
Bottom line is, if one has the room in a cardboard rocket with motor ejection for a Jolly Logic Chute Release, it will likely allow more protection against zippering with a too early or late ejection. RS after several runs had suggested a 14ft/sec rate after
apogee when the chute deployed. It was so far up, I couldn't tell if that was the case. It just seemed to hang in the sky for a moment.
Kurt