I recently upgraded my gen 8 m4a1 to metal gears 18:1 and a 1.2mm spring new inner barrel new cylinder and head but after a few shots it gets jammed and is double feeding the gels what csn i do to make it stop someone said i could short stroke the tappet or glue the rubber nozzle on to the cylinder head anyone have any ideas or suggestions to help me
Make sure you have Gelblaster gear set and not Airsoft type.
Gelblaster gears have the tappet plate pin on the sector gear in a different orientation to Airsoft gears.
The gelblaster gear pins are a different position to allow for earlier and longer travel timing to give extra space to feed 7-8mm gels, rather than the quicker/shorter tappet travel/timing required to feed 6mm BB’s.
Compare the tappet pin location on your new gears against your old gears and see if they are different.
If the gears have the Airsoft pin, then nozzle travel/timing will not allow gels to feed properly and cause jamming in the t-piece 
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Ok Doc thanks im gonna check my gears now and see.
No worries mate 
Hopefully you can find some results and let us know how you go.