Just my 2 cents....I’ve been finding a relatively consistent 1% variance when sorting a few different manufacturers and calibers, however most pellets are within 1/2% of the stated weight, measured 3x to 2 decimal places and then rounded up/down. (Ex. 19.58 would be rounded to 19.6) In regards to head size, try a pelletgauge instead of calipers. From my personal experience, you may get a different reading using calipers if you turn the pellet a few degrees. Others may disagree.