I went with the specs I could find on the Estes BNC-55AC nosecone. I haven't had one to model from.
Length (exposed) 5 3/8"
Shoulder Length 3/8"
OD 1.325"
However, Earl posted a very clear photograph of the supplied nosecone with his kit.
https://www.oldrocketforum.com/showpost.php?p=238417&postcount=20