Specna Arms M16 DMR 5.1 Two Spring are included with shottie Two Spring are included with the AEG one that will give 410 ideal if going DMR and locking to Semi (Gate Warfet is ideal for this) and a more friendly Spring that gives around the 320 mark This rails became famous with the US Navy SEALs unit “DEVGRU” or known as SEAL Team SIX the unit who was on the Bin Laden raid and several other secret missions The gearbox which is reinforced on the height of the cylinder’s head hides a steel main spring guide and also 8mm ball bearings and steel thread wheels which are placed on spacers fixed stock which holds the battery and the pistol grip were made of polymer plastic