I have found that bullets do seem to vary in weight, kb
Well, you forced me to do it!
I took the covers off my RCBS 5-0-2, RCBS 5-0-5 and RCBS 10-10 scales.
I broke out a box of .224 Sierra 52 grain HPBT bullets and weighed each one on each scale...
What did I find?
All three scales read exatly the same, and the range of bullet weights was between 51.9 grains and 52.0 grains, with 92 of them weighing 52.0 grains!
Now, if you ask me, that is pretty damn good, but then I really don't find a 0.19% error all that critical in reloading.
So them I took a box of .284 Sierra 168 grain HPBT bullets and did the same. Guess what I found? weights ranged form 167.9 to 168.1 grains with 90 of them at exactly 168 grains!
Just in case you are interested the lot # of the .224 bullets is 2051938, and the lot # of the .284 bullets is 128314.