Shock Cord Length

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...I pulled up an OR sim of the Cherokee E. Reduced the overall length of the airframe by 50 percent and added 10 grams of clay to the tip of the nose cone to get stability back. Same basic rocket.

Slight threadjack:
I'm such an OR nerd. I've just cleaned up this sim. Consolidated to a single BT, shrunk the chute to 15 inches, added a baffle and a boat tail. Neat little rocket. 2000 ft on an E12-6 you can buy at Hobby Lobby. I'll probably have to build it one day, as I do expect to have a spare Cherokee E nose cone left over from the PNC-55 nose cone pack down the road. It's already named the "Chero-K": shortened Cherokee, and -K for "kurz."
Just pondering this a little. Much like "calibers" for stability factor, this seems to be a rule of thumb that's based on an assumption about an "average" rocket, but in its conception switches from the relevant variable to another one that doesn't directly bear on the objective.
I had the same idea. I was trying to determine the length to use for LPR and decided that the average LPR for me would be about 2'. I've seen HPR use what appear to be excessively long shock cords but they work so I did the same thing and settled on 10' length. If everything deploys as designed it appears from the ground that the body tube has separated from the chute, until it drops far enough to get to the end of the 10' cord.
Yup, that's why it's a rule of thumb rather than a set rule.

I currently make hybrid shock cords using elastic from Estes kits and a comparable length of Kevlar. Together, they don't follow the "3-4 times body length" rule of thumb, but they work for me.
I'm getting a pretty big pile of Estes rubber shock cords so I'm thinking about trying that myself.
I'm getting a pretty big pile of Estes rubber shock cords so I'm thinking about trying that myself.
I use this hybrid approach because like you, I have many Estes elastic shock cords laying around. I love finding "new" uses for spare parts/materials, especially if it helps me avoid spending money.