Dual springs vs single springs could cause a brightness difference too, along with batteries of course.
All Q8s feature dual springs from what I have seen.
So I just noticed this on my latest Q8. The screw isn’t missing, the head is snapped off. Fine QC, Thorfire :+1:
ouch that isnt good 
It has always been predicted that later batches of BLF lights after the group buy could suffer from decreasing QC. The Q8 still holds up well to newer flashlights on the market so if Thorfire is smart, they keep up the quality.