Ok, I'm busted. So this is the Tomahawk part of a Semroc Nike-Tomahawk. That's "why" the odd sized components. I am investigating making it a two stage rocket. As designed, it is a only a single stage.
I am looking at using all the Tomahawk parts and using the motor mount tube that would be installed in the booster in the Tomahawk. All I need is some centering rings for it and the sustainer will be done. Oh, and I will probably use the chute that came with the kit in the sustainer (Tomahawk) after I either cut it down or cut out a spill hole in it.
I need the motor to stick out 1" so that it can engage the booster. I was thinking of "flipping" the body tubes and using a longer coupler so I can turn the coupler into a baffle. I need to see if I have a longer one in my spare parts box. I like your idea of having the rocket split between the "motor" and "payload" sections. I'll play with that in Open Rocket
I also enters an ejection delay, but I don't know how to ask it to tell me if a seven second delay is good or not.
So the purpose of this exercise was to see if the sustainer could fly on it's own and it seems it can.
I just moved the separation point and it still looks good.
Thanks again for the help and ideas.
Now I need help figuring out how to add the booster in.
-Bob