Thanks for the reply. I did further experiments.Please take a look at this: Voltage Drop - Not Where You Think | atmizoo vaping modware
If you are measuring with the same battery and atomizer but still get worse readings with the Roller, then you can do the following:
1) Clean the spring with a de-oxidant or remove it altogether.
2) Clean the battery-side contact with silver-cleaning cream (not the internals of the switch)
3) Clean the (brass) 510 connector threads (in & out) with a de-oxidant.
If you are still having issues, I'd suggest sending the device back for a check!
When using 18350 the drop is the largest 0.67 volts on load. When using an 18650 the drop is less, around 0.40 volts. So I removed the washer that was on the bottom cap and the drop became only 0.20 volts which is the best of all my other mechanical mods. I am assuming that the washer is preventing the spring from bending all the way and making best conductivity and in the 18350 mode I think the spring is the most expanded which makes it the worst conductivity. I don't want to remove the washer and I think the spring should not be compressed to the max since it will not work as a hot spring anymore and protect against shorts. Am I right? What is the solution then?