A vacuum bag (18) is placed around the inner forming surface (IML) of an inner mandrel with radially retractable sectors (11a, 11b) having parallel longitudinal slots (17) with composite stringers (30) in the slots (17). An inner support (31) in each stringer is covered by an impermeable tubular bag (32). A composite skin (37) is laminated around the stringers (30), the coated supports (31, 32) and the inner forming surface (IML). An outer curing tool (50, 51) closes around the skin (37) defining an fuselage barrel outer forming surface (OML), leaving an annular gap (G) between the skin outer surface (37) and the outer forming surface (OML). Vacuum is applied between the vacuum bag (18) and the outer tool (50, 51), enlarges the uncured barrel diameter, releasing the barrel from the inner mandrel (10) and bringing the skin outer surface (37) into contact with the outer tool inner surface (IML).