I weigh almost all bullets I cast.
Every 2 cavity mold I've ever owned cast bullets of two different average weights. I mark the mold cavity with a tiny punch mark on the nose so I can tell the two cavities apart.Mark/no mark or front mark/rear mark. I mark cavities with a Lee decapping rod pointed end and a hammer. Less is better here.
30 caliber bullets from the same cavity will weigh +/-.3 grains. Ex: 205 gr. average, with weights varying from 204.7 gr to 205.3 gr. Variation greater than this tells you that there's something odd going on. With everything cooking right variation will be less, with most bullets +/- .2 or even .1 gr.
Does weight matter? With lots of bullets from the same cavity and variation of +/-.3 gr., I have never been able to reliably detect an accuracy difference between bullets sorted into .1 gr. sets and those mixed. Ex: Sorted sets of bullets weighing 204.7 or 204.8 or 204.9...or 205.3 vs. mixed bullets from the same cavity weighing 204.7 to 205.3 display no reliable detectable accuracy difference in rifles shooting <1” 5 shot 100 yard groups, averages of five groups. If your gun shoots, and you're happy with 2” 5 shot 100 yard five group average, weight doesn't matter if the bullest are inspected.
Why weigh? It lets me identify and re-melt the stragglers, the bullets outside the norm. Ex: With bullets from one cavity bullets weighing 205 gr. average and most +/-.3 gr., now and then there's a bullet weighing 204.2 gr. or 206.0 gr. Something is different with these, and I use these for sighters/warmups or put them back in the pot.
This is based on records of 24,628 cast and weighed bullets.
joe b.