I've been using a lot of American Eagle brass I've kept from shooting factory ammo in my 223. For the most part, those Federal (FC) brass has been by far the most consistent by weight compared to my Hornaday and Winchester brass. One of my current loading blocks consistes of 100 FC brass all weighing between 92.0 and 92.5 grains. My newly purchased 100 pcs of Winchester 223 brass is barely within 2 grains and I had to toss a few due to neck wall defects.
I have not performed a water capacity test yet, but plan to. Not sure it's even necessary on such a small case.

One thing I noticed with the most recent American Eagle brass I have as compared to year old brass is the flash hole placement. None of my most recent AE brass has flash holes that are centered in the primer cup. It's all off center by at lease a little, to as much as 3/4 hole diameter off center.

Older brass is much more consistent, and Hornaday brass seems to be very consistent, albeit a bit soft.

Not sure how much this effects powder ignition in a small case, but it's the reason I'm trying to buy higher quality brass. Someday I may have to bite the bullet and buy Lapua.