A method and system of manufacturing a needle-less injector to deliver an injection having a pre-determined injection dosage. The method and system include providing an injector housing, installing a compressible coiled delivery spring within the housing, and selecting a hammer having a length from a plurality of alternative hammers having different lengths, wherein the length of the selected hammer corresponds to the pre-determined injection dosage. The method further includes installing the selected hammer within the housing in contact with the compressible coiled delivery spring and further in contact with a syringe plunger such that upon assembly of the needle-less injector, decompression of the compressible coiled delivery spring causes the selected hammer to move laterally, thereby causing the syringe plunger to move laterally within a needle-less syringe to provide an injection having the pre-determined injection dosage corresponding to the length of the selected hammer.
