04-01-2018, 11:45 AM
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SPEV/Orion wrangler
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Join Date: Mar 2005
Location: Atlanta, GA
Posts: 2,645
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Quote:
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Originally Posted by tbzep
BT-30 is an old Estes size.
OD: 0.767
ID: 0.725
Not sure where BT-20+ originated.
OD 0.770"
ID 0.744"
eRockets (Semroc) has both.
You can take a regular 20-55 centering ring and sand it until it fits. Otherwise, print out a template and cut your own. I seldom buy centering rings anymore. I usually make them from cardboard or balsa.
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BT-20+ may be what CMR called RB-77. Their regular tube was RB-74, and RB-77 was a slip-fit over it. Apogee (Ed LaCroix version) had similar sizes of their BlackShaft tube (and maybe their regular tube too)
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Roy
nar12605
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