How to pump same amount of paste every time?
This thought came to me, and is so different from my first answer I don't think it makes a good edit to that...

If the product is really 


  made of pepper flakes in an oil


rather than mix a batch at all, measure out a bottle's worth of each, funnel in the flakes, pour in the oil (and seal/heat-process if that's normally done.) Might need some vibration/shaking, but two easily dispensed components mixed in the bottle might be a lot easier than getting the mixture nicely dispensed.