If I understand you Mack, the stamped/mandrel bushings fit against the end of the tube and everything slides on the mandrel's "axle". Some bushings for the larger pens and items do fit inside the tube yet push against the end of the tube as well as slide on the axle of the mandrel. So the bushings you use for mandrelless (no mandrel) turning basically are stepped bushings that can easily be solid metal as long as they have a center dimple for the centers (be they live or dead). Thus the bushings fit into the tubes, push against the end of the tubes, fit between the tailstock and head of the lathe, no mandrel used/nor could one be used if you wanted to with these bushings.
Even though I have never turned without a mandrel, is this the process?
Personally, I have not had problems unless it were man made by me, so will stay at this time with my mandrel as I already have hundreds of sets of bushings!!