The F2 nozzle is spring biased forward which provides a uniform loading force no matter operating pressure. It shares an equivalent spring because the Fusion Engine with both light and heavy spring options available to regulate the loading force. the planning of the F2 allows for an operating pressure range of 45psi to 145psi for CQB to DMR speed options. As a result, just one nozzle is required for the whole velocity adjustment range. This model is meant for the Classic Army M249 series.