Ouch! I hate to be the bearer of bad news but weighing the completed cartridges is unlikely to be successful for you in culling the over-filled cases. Depending on if you've sorted your brass by head stamps, the brass can vary by around 2 grains for the same head stamps and up to 8 grains for mixed head stamps. I wouldn't do that and feel very safe. I would have to recommend pulling the bullet heads, dumping them and re-throwing the powder from a more accurate scale or powder feed. -S2

ETA: here's a link to an earlier post that I did to show the differences in casing weights:
Some (probably useless) Brass Facts