Chinese Bulldog extruder enhaced (a.k.a. triying to make it good)

So! i bought this bulldog, thinking: nice! is cheap and it seems to be good! but no.
those friends from china copy this extruder and, the copy it bad. baaaad.
so i use the extruder without spring, for a year now and it works well, but i need some sort of spring inside for compensate the difference in size of the filament, and... it came to this

you will need:
6mm grub screw or blind allen screw.
5mm spring (i use the ones who comes with the bulldog extruder)
all the parts above

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