Sirius Rocketry had some single Estes ones that I ordered.You reqlly took my suggestion and ran!
Where will you get a 2nd nosecone?
Also, using the stock mean machine fins (even with your additions) looks a little small to be effective for this much shorter rocket
I tried it with a pod but couldn't get the pod to move up to the same height as the main tube. I ran it anyway and it went well. I am not at my computer but I think the double went 100 ft higher at around 470ft?I think rocsim can do the double things, Im qilling to bet it has to do with Pods
If i was doing it in OpenRocket, Id make a tube with the same cross sectional area as the two tubes, cluster mount, and override the mass to match