If you are using multi-cavity moulds from Lee, you will get some variation in diameter and weight from each cavity. 002" variationis too much. 2 gr of difference isn't bad for pistol bullets.

Lee moulds need a little tweaking and breakin to get tem to cast well. go here: http://castboolits.gunloads.com/showthread.php?t=654 and do exactly what it says to do, it takes a little time but is worth it. I do this tweaking on all of my Lee moulds when I first get them.

If that doesn't work and you are still not filling the moulds out, try running your melting pot hotter and preheat your mould by casting several bullets in quick succession or setting your mould blocks on top of your melting pot for a few minutes. If this still doesn't work, add a bit of tin to your pot- I use about a 1' length of 50/50 soldering wire which is usually enough to get even skinny rifle bullets to fill out. A lot of references say to use about 1lb of 50/50 solder for every 10 lbs of alloy, especially wheelweight alloy, but I find this to be overkill- the tin is only meant to make the moulds fill out, and its expensive.