From your question, I believe you are asking if these things can be used in a modern in line. If so: Yes you can use loose powder, and yes, some saboted bullets are soft lead, others are jacketed. Most use a jhp. You cannot, to my knowledge use a jacketed bullet without a sabot. Maybe there is something I don't know of. You can, however use a conical lead without a sabot, one that fits the bore. These must of necessity be soft lead. All are used in different situations effectively.
Ben