small pointers that could help you out.....
Even with carbons, it is helpful to role them first on something like a piece of glass, old mirror or anything nice and flat and preferably wide enough to let the full length of the shaft contact that surface while rolling. Even with carbon (you'd assume would be perfectly round and straight) you could be surprised. If you have a spine tester, you might want to also spine them and maybe group them - separate what you think might be the best from others you think might not be so. Good shafting will show little to no variation that is of any consequence.
You typically pay more for carbon that is marked straighter (.003 vs .006) Role your carbons on that surface. A .006 marked shaft might role better (straighter) after cutting a 1/4 off the NOCK end while in a bare shaft state before fletching. I have read, been told, and have experimented and experienced myself, that carbon shafting can have run out on the ends, could or does happen while in production, depending on the shafting (model, brand). You are going to cut the point end when you get ready to install inserts. Trim the nock end a touch first, then go for your build to total length from there. This is my experience and the way I build carbons- just my 2 cents.