I think a BT-70 or 80 would look good.
OK, BT-70 sounds good.
The diameter of the printed out sea-sting is 11mm.
On the Apogee sales page for the sea-sting it is stated that the nose cone is a true three to one ogive.
11mm (diameter of the printed out sea-sting) X 3 = 33mm.
The entire length of the sea-sting (on the printed out sea-sting picture), plus the nose cone is 221mm.
Subtracting the length of the nose cone (33mm) = 188mm.
The desired BT is a BT-70. This tube has a outside diameter of 2.217 inch or 56.3118mm.
(2.217 inch. multiplied by 25.4mm (1 inch) = 56.3118mm).
Now the scaling factor can be determined by dividing the desired tube size (2.217 in) by the tube size of the sea-sting in the printed out picture, (11mm).
56.3118mm divided by 11mm = a scaling factor of 5.1192545
you can round that number up or down, or use as is.
With the scaling factor now know, take the length of the BT in the print out the sea-sting and multiply it by the scaling factor. 188mm X 5.1192545 = 962.419mm. Divide that number by 25.4mm (1 inch)and you get 37.890 inches. That's the length for the BT-70 upscale.
www.erocket.biz has a balsa 3:1 BT-70 nose cone available. I kinda like the 4:1 nose cone myself.