Never settle for less than the best, this Systema M4 Expert Full Tune Kit is everything that you need to upgrade the inside of your gearbox. This kit comes with the following:
Genuine Ratio Helical Gears
Silent Head Set
Smooth Bore Cylinder
Metal Spring Guide w/ bearings
Metal Ball Bearings
This upgrade kit comes with everything inside the gearbox except for the switch assembly. There is no better way to upgrade the internals of your M4 than to get this Systema Full Tune Kit.
Professional installation highly recommended.
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