Geissele MPX Recoil Springs
During extensive testing of the MPX weapon system it was determined that the bolt speed in these systems is very high. Geissele Automatics feels the best way to increase the life of the trigger and the rest of the operating components is to tune the recoil system with different spring rates depending on the ammunition type being used.
Geissele ships the trigger with three spring weights: they are about 30, 45, and 55% stronger than the stock recoil spring. It is recommended the shooter choose the ammunition they plan on using and function test with the supplied spring sets. For optimum performance, the weapon must use the heaviest spring set while still providing full functionality.
To select the best spring we recommend starting with the yellow spring set and testing for proper operation. To test; shoot a magazine of 5 rounds observing the ejection pattern and if the bolt locks back on the final round. If this is successful shoot 5 magazines of 1 round each to observe if the bolt locks back on the last round. If the bolt fails to lock back or weak ejection is found then move to the lighter spring set which is painted red. Conversely, if the shooter feels the operating system is still too violent moving to the heavier spring set (indicated in white paint) can be tested for functionality.
