The build up of brass on the tubes suggests that you didn't heat the shell enough before starting to add the brass. The thin tubing heats much faster than the thick shell, so the brass will tend to pool out on the tube before going into the joint. Keep the flame on the shell until it's fully hot before hitting the flame on the tube. That way when the brass melts, it gets pulled into the joint right away without so much pooling. This was right after washing off the flux, before any finishing: