I setup a simple rocket in openrocket with a body to fit the engine and a nose cone. I did not add fins. This puts the center of pressure up in the nose cone way ahead of the center of gravity. What I am trying to do is setup a situation where you would use gimbaling to stabilize the rocket but in an environment where it may not be necessary so I turned off wind for the simulation. The rocket still goes unstable and I'm curious why. It seems to remain unstable until I make fins large enough to move the center of pressure behind the center of gravity.
It appears I can remove air pressure in which case the simulation does work, so I'm guessing there is some non-uniformity somewhere?