Case Segregation: Neck-Wall Thickness

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This is a specially-adapted excerpt from the forthcoming book, “Top Grade Ammo,” by author Glen Zediker, owner of Zediker Publishing. Click here to order from Midsouth.

by Glen Zediker

“Segregation” is sorting and separating. If someone is looking for the best performance, which, in my mind, is the most consistent performance, from stock-on-hand, then it’s a worthwhile chore. However, it is a chore. Keeping that in mind, the item below hopes to help a handloader decide how to proceed when there are 100 new pieces of brass set out on the workbench.

I segregate new brass for my tournament rounds. The “tournament” is NRA High Power Rifle. That’s fired at 200, 300, 600 yards. Clearly, the “best” of my brass goes to the 600-yard-line. I do this with new brass because, as I said in an earlier installment, cases should be kept with the same load, and I want to know my best cases before I fire-form with my 600-yard load. Keep same for same.

The questions are: How many piles do you want? and What criteria do you use?

This is an old photo of my segregation results on 100 WW-brand .223 cases. These sized cases were checked using a runout indicator. Here’s how it broke down, left to right: 7 were “flatliners,” under 0.0005; 32 were under 0.0010; 37 were at 0.0010; 18 were up to 0.0015; 6 were over 0.0015; none were more than 0.0020. That’s pretty good, as far as I know. Seems good. I need a total of 88 rounds for a tournament, so I had confidence in this brass. Tip to make your sorting easy: Go to a discount store and get a few small containers, something suitable to contain several cases. Get some masking tape and write the criteria or content (after you sort enough to get a range) and mark the containers. Then just pitch each case into the suitable container as each is measured.
This is an old photo of my segregation results on 100 WW-brand .223 cases. These sized cases were checked using a runout indicator. Here’s how it broke down, left to right: 7 were “flatliners,” under 0.0005; 32 were under 0.0010; 37 were at 0.0010; 18 were up to 0.0015; 6 were over 0.0015; none were more than 0.0020. That’s pretty good, as far as I know. Seems good. I need a total of 88 rounds for a tournament, so I had confidence in this brass. Tip to make your sorting easy: Go to a discount store and get a few small containers, something suitable to contain several cases. Get some masking tape and write the criteria or content (after you sort enough to get a range) and mark the containers. Then just pitch each case into the suitable container as each is measured.

In sorting cases, the finer the increments that define what you assess are Grade A, B, C (and possibly D, E, and F) cases, the greater the range encountered, and the fewer single examples that will occupy each group.

Establishing criteria limits (defining the contents of each pile) comes mostly from experience in checking examples of the stock. One thing you will learn from segregation is what the component is “supposed to be.” You’ll see a pattern. The more you measure, the more you’ll learn, and it will help to establish the criteria you end up banking on.

For me, I sort by wall-thickness variation, specifically, case-neck-wall-thickness variation. All other things being the same, and the tooling being what it should be, consistent case-neck walls result in bullets looking into the dead center of the rifle bore. Some call it “concentric,” and I do too.

You’ll need either an “inside” micrometer (which has a ball-end, made for tubing measurement) or, way faster and easier, a specialty fixture that incorporates a dial indicator. The micrometer will be more precise because it will provide a number in the 0.0001’s, but that gets back to the realism of the criteria. A quality dial indicator still shows less than 0.0010 variations, just look at the needle position between whole marks. Measure at 4 points around the neck. My expectation is “0” for my 600-yard brass: no variation, which really means I accept anything that’s under 0.0010. I end up with piles in 0.0005 increments: less than 0.0010, 0.0010, 0.0015, 0.0020, and any larger doesn’t get fired in competition. I do this because it’s direct and fast, and because I am looking for good, better, and best case groupings to coincide with my needs for 200, 300, and 600 yards.

This appliance is from Forster and is pretty versatile. Purpose-built, single-station tools are a little better to use, but, all around, something like this serves most well.
This appliance is from Forster and is pretty versatile. Purpose-built, single-station tools are a little better to use, but, all around, something like this serves most well.
Here’s how to use the tool to check wall thickness. Zero the indicator against the pilot/spindle and then read the dial with the case neck over the spindle; position the indicator about halfway down the neck. I read it at 12, 3, 6, 9 on the clock face. Understand that wall thickness variation and runout are related, but not directly.
Here’s how to use the tool to check wall thickness. Zero the indicator against the pilot/spindle and then read the dial with the case neck over the spindle; position the indicator about halfway down the neck. I read it at 12, 3, 6, 9 on the clock face. Understand that wall thickness variation and runout are related, but not directly.

If I get lazy, which is more common now than not, I size all the cases (to get the necks shaped up) and then check runout at the neck on another specialty tool: a concentricity fixture (some call it a “spinner”). The system I’ve been using here of late serves both duties. Make sure to have run some sort of inside-neck sizing appliance, either an expander in the sizing die or a mandrel after the fact. If not, the results will not be viable. This explanation isn’t too detailed, but the variations get “pushed” either inside or outside depending on the last tooling the case neck was treated to, and it needs to be pushed to the outside.

Does it really matter? Yes. There have been tests done by many trying to establish the point where wall variations or runout influenced group size. Since this point varies in different tests I’ve seen, I have to believe that the rifle/ammo combo has a mighty influence. It’s very likely that the better the package, the more sensitive it will be to showing up variations. I do know that when Hornady tested this at 200 yards (on their indoor range), they found that variation in wall thickness of 13% had a significant influence on group sizes; in this instance, that equated to about 0.0015 inches variation.

Reposition the hardware to check runout. This is not as precise as measuring thickness, but, in another way to look at it, provides more of a “what you get” evaluation. A 0.001 wall variance does not directly equal 0.001 measured runout. The basics of segregation: you can only find what you’re looking for. One tip: I get my most consistent, most accurate results by lifting and re-seating the indicator at each point I want to check rather than actually spinning the case and watching the indicator needle movement. It’s easy to check loaded rounds too, as shown. There’s a good deal of wobble in many factory loads, and if you rely on it for important shots (like on a big hunting trip) sometimes it’s good to know that you have the best-of-the-box in your pocket.
Reposition the hardware to check runout. This is not as precise as measuring thickness, but, in another way to look at it, provides more of a “what you get” evaluation. A 0.001 wall variance does not directly equal 0.001 measured runout. The basics of segregation: you can only find what you’re looking for. One tip: I get my most consistent, most accurate results by lifting and re-seating the indicator at each point I want to check rather than actually spinning the case and watching the indicator needle movement. It’s easy to check loaded rounds too, as shown. There’s a good deal of wobble in many factory loads, and if you rely on it for important shots (like on a big hunting trip) sometimes it’s good to know that you have the best-of-the-box in your pocket.

There is another popular and viable means of segregation and I’ll work that one next time. How you choose to segregate brass does have something to do with what the ammo is ultimately used for.

 

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4 thoughts on “Case Segregation: Neck-Wall Thickness”

  1. High quality brass costs at least double, but it’s much more consistent. Make sure cases are same manufacturer, same number of firings, same case length, and check and trim with an inside the neck turner. Some weigh cases, bullets and use match quality primers to make every round as consistent as possible.

  2. Can these sorts be repeated in 24hrs. and end up with the same groups? How much creep is there over the period? How much intermixing if any are you seeing?

  3. Will turning the outside of the necks to the same consistency give the same result?

    1. I question the suitability of trying to sort case neck thickness to four decimal places using instruments accurate to three decimal places. This sounds like voodoo to me . Trying to sique ones self into something. I also asked the question whether the sort was repeatable. I personally find that many of these kind of exercises are not repeatable and much of this fine sorting is a waste of time. Grosser categories are more reliable.

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