I tried launching it with a 7-orange-tank triple-layer asparagus section, and then I tried (in two different designs) a nuclear stage and a Rockomax X-200-16 with a Poodle engine. Both times it failed to circularize, and I had to revert the flight. Here's the craft, sorry you can see the rest of my screen - cropping fail. I do try to start my circularization right at my apsis. Maybe I should try replacing the Rockomax X-200-16 with an X-200-32, like DisarmingBaton5 said, and burning early? I'm normally very good at orbits.