I sat down today and decided to try weighing out some .223 brass (winchester), to see how much of a difference it would make in my group sizes if I "batched" those that have very similar weights. All brass are of the same original case, once fired, de-primed, FL sized, trimmed & deburred, flash hole reamed etc.

When I went to weigh them, I couldn't believe the difference in weights from one case to another! I checked to make sure there was no tumbling media in the cases and even brushed the inside of the necks again to see how much of a difference that would make, which was nil. Out of 25 cases the best consistency I could find was three cases within 2.5 gn's

Is this normal, or do I have a lousy batch of brass? What is the "normal" consistency I should expect for picking out 20 pieces of brass from 100 for consistent weights?

There's a reason that some guys start with 1000 pieces of brass just to get 100 that "match", and you've just found it. I started with about 750 (30-06), and culled down to 200 "keepers" that have a 10gr total spread (I keep them in seperate boxes by 1 gain increments, so that all cases in one box are +/- 1/2gr).
Internal water capacity is a more accurate way to "match" cases (and a even bigger PITA) as it ignores variances in the extractor groove.

I used to do a lot of case weighing, there is a lot of difference between the heaviest 06 cases and the lightest. I don't shoot any BR or even heavy varmint rifles. With my most accurate hunting rifles I can get .75" groups, occasionally .5". What I found was weighing cases wouldn't make much difference in that grade of accuracy. If I keep the headstamps alike usually the variation isn't enough to affect "good" hunting accuracy.

I do weigh my 223 brass to segregate heavy brands from light mfgs. For instance Fed brass weighs around 96 gr. whereas WW Supers weigh 90. I lump my cases into heavies and lightweights by headstamp. Then the heavies get 27.3 gr of W748 while the lightweights get 28.5 gr. Don't know how much accuracy is affected, but the heavy cases won't hold 28.5 gr of 748 without overflowing.

Thanks for the reply!

Interestingly enough, 27.5 gn of 748 has been the load for me in a Savage .223 w/ Accutriger. With that load, I've been able to put .35" 3 shot groups fairly consistently and 5 shot groups are well under an inch if I do my part.

I'm wondering how much of a difference it makes to weigh out a "select" batch of brass? Not to mention where to begin picking a starting weight?!

How about water capacity? How would you go about measuring it?

It's fairly easy to check water capacity. You want to do it with fired cases. Measuring new, unexpanded brass tells you very little. What I do is to take my fireformed case which is trimmed to the correct length. Weigh it with the fired primer in it. Then, with a dropper, fill the case with water into which you have added a drop or two of detergent. This is to better uniform the meniscus when you fill the case. Add water until just before it spills over the mouth. I put my cases right on the digital scale and keep adding until you get a uniform meniscus on the top of the mouth. Read that weight and subract the dry weight of that same case, and you've got the water capacity. It's fast and easy. Measuring a couple of cases in the lot you are using usually shows little difference in capacity if they are all within 1% of dry weight.

All the internal ballistics programs I know utilize the full case capacity for their computations. You'll find that even one or two grains of dry weight difference in cases won't make much difference at all in the internal capacity. Once you get over about a 1% disparity in dry weight you'll have a couple of tenths of a grain water capacity difference, which is truly negligible for your purposes. Over 2-3% and you'll note significant differences. As an example, 300WSM brass expanded to 338 has a water capacity of 83.7g in Winchester brass, which weighs 230g dry. Norma brass which weighs 250g in the same configuration, has water capacity of 81g. That's a significant difference.

I usually weight sort each lot of new brass to within about 2%. The only case prep I do before fireforming is uniforming the primer pockets. After fireforming I trim to the length of the shortest case, deburr flashholes, and then check dry weight uniformity again and sort to 1% tolerance. I then check water capacity of each lot. It can and does make a difference if seeking extreme accuracy. I agree that for run-of-the-mill hunting loads it's a lot of work for not much gain.

I further sort brass after all the prep by firing it. Occasionally you'll find a case that in spite of being uniform, still throws a flyer. I mark it at the range, and fire again. If it does it again, cull it. I understand the benchrest boys aren't bothering much with sorting by weight or water capacity, preferring to fire sorting their brass. But then they are usually using high quality Lapua, or similar brass which is quite uniform to start with.

Don't waste your time weighing brass, for the most part. It doesn't pay real dividends. Just throw out any case that gives you flyers on an established good load. Shoot only same lot, same headspamp cases.