Abstract: Undercap filler machine and method for cyclically vacuumizing product-containing, conventional spray can type aerosol containers, charging metered quantities of compressed gas propellant thereinto, and crimping valve cap assemblies thereon. By means of sequencing spring action on the crimper head, the machine and method provide (1) accurate control of the cap lift against relatively low sequencing spring force during charging with compressed propellant gas and (2) firm cap seating under relatively high sequencing spring force on the bead of the container opening against the internal pressure therein during crimping. The controlled cap lift during charging introduces a temporary throttling restriction in the form of a predetermined narrow annular orifice between the fill chamber of the crimper head and the interior of each container which orifice produces a controlled drop in the impact gassing pressure and increased velocity of gas flow into the container.