I do a lot of what the article Wynne posted. Although I do not agree with Step 8! I just completed sorting 100 formed .300 Atlas cases. I used Norma brand .300 Weatherby cases charged with 14.0 grains of Unique, filled w/ Cream of Wheat (CoW) and topped off with toilet paper. Hopefully you will be able to view the attached excel spreadsheet. After fireforming, I trimmed all of the cases to the same length. I left the spent primers in the cases and numbered them 1-100 w/ a sharpie. I weighed each case and recorded it on the spreadsheet. Then I filled the cases with tap water to the edge of the case mouth (used a paper towel to absorb the convex water above the mouth). I weighed each case again and recorded it on the spreadsheet. The spreadsheet calculates the capacity for me. I will say that I think Rubbing Alcohol would be a slightly better medium to use, rather than water. If you look at the three different tabs you will see why I don’t agree with just weighing the cases. Case plus spent primer had an extreme spread of 2.1 grains. 1.1 grains is .5%. Capacity of water on the other hand had an extreme spread of .8 grains. That .8 grains is less than .5% variance throughout the lot. What does all of this tell you? It tells you that weighing just the case will not tell you where those weight differences are, is it in the Belt, Extractor grove, Head, Body, Shoulder or neck?
I only use either Lapua or Norma brass. With Lapua, I ream the flash holes prior to forming Dasher or Odin cases. I use the CoW method but with 8.0 grains of powder for a 6mm. On the Thor and Atlas cases I use 14.0 grains and do not ream the flash holes. Both are Norma cases and Norma drills the flash holes. Also I do not uniform the primer pockets to depth until I’ve shot one bullet through the case.
I anneal after each firing. Using a propane torch, drill and Sinclair case driver.
I would recommend just go put some rounds down the tube. Work on your load however many pieces of brass you will have for that gun. Get your cases formed and then sort!
I hope this helps you.