Firefox sells a body tube that is dimensionally the same as a BT-40, but spiral wound.

Unfortunately some stupid regulation prevents them from shipping it in decent lengths. I can understand why convolute wound tube has those rules, but this isn't something you'd use to make fireworks.

Until that scotched my order, I was set to put together a couple of dozen models based on those Design Book plans.

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NAR #27085 - Oregon Rocketry - SAM