On mine I decided to use a BT-60. It's all one piece until the middle of the 3rd stage. Then the 3rd stage necks down, but the payload section was exactly the OD of a BT-60, so a different BT-60 completely substitutes for the original paper tube. Which makes it great for nose cones...the one you see was simply glued to a BT-60 stage coupler. If I find it too complex to build the rest I can always go to BMS to make an entire nose cone...
The main reason I did this was for strength...I've found that BT-50s or BT-20s tend to get 'tender' in the long axis much past a standard 18 inch length, and I wasn't sure how much side force these shrouds would impart. I also plan to run a BT-50 along the whole length of the rocket for additional strength (this rocket will be very Russian...robust). This will allow me to use Es to Bs (with adapters) to fly this one. In addition, the launch rod will acutally run through the BT-60 and through the nose cone shroud. The BT-50 will actually be carrying all the ejection charge until the nose cone (which will have a BT-60 stage coupler but a BT-50 balsa block).
The things you lose with using a wide tube is the six inner engines on the first stage, and the 4 engines on the third stage. But considering this'll be more of a semi scale project (I plan to fill and sand, then add most of the larger details, then primer and paint), I can accept the compromise.
Hopefully she'll turn out to be a good flier.
FC
