I weigh cases then check case volume. Case weight does not give an accurate indication of case volume. Case volume in (my opinion) is where the difference lies. I write the cases weight down then fill cases with alcohol and weigh again. Subtract case weight from gross weight and you have case volume. I keep my case volume within .001 gr. Bullets even though the box says 220 gr not so for all. Bullet weight will vary within a given box. It just depends on how far you want to go with this. Then there's neck turning which centers the bullet to bore adding to accuracy. Sorry got carried away. Oh and the reason I use alcohol is that the residual in the case evaporates rather quickly.