May 5th, 2017

Bullet Concentricity Basics — What You Need to Know

Sinclair concentricity 101 eccentricity run-out reloading plans

Sinclair International reloading toolsSinclair International has released an interesting article about Case Concentricity* and bullet “run-out”. This instructional article by Bob Kohl explains the reasons brass can exhibit poor concentricity, and why high bullet run-out can be detrimental to accuracy.

Concentricity, Bullet Alignment, and Accuracy by Bob Kohl
The purpose of loading your own ammo is to minimize all the variables that can affect accuracy and can be controlled with proper and conscientious handloading. Concentricity and bullet run-out are important when you’re loading for accuracy. Ideally, it’s important to strive to make each round the same as the one before it and the one after it. It’s a simple issue of uniformity.

The reason shooters work with tools and gauges to measure and control concentricity is simple: to make sure the bullet starts down the bore consistently in line with the bore. If the case isn’t properly concentric and the bullet isn’t properly aligned down the center of the bore, the bullet will enter the rifling inconsistently. While the bore might force the bullet to align itself with the bore (but normally it doesn’t), the bullet may be damaged or overstressed in the process – if it even it corrects itself in transit. These are issues we strive to remedy by handloading, to maintain the best standard possible for accurate ammunition.

The term “concentricity” is derived from “concentric circle”. In simple terms it’s the issue of having the outside of the cartridge in a concentric circle around the center. That goes from case head and center of the flash hole, to the tip of the bullet.

Factors Affecting Concentricity

The point of using this term is to identify a series of issues that affect accurate ammunition. Ideally this would work best with a straight-walled case; but since most rifle cartridge cases are tapered, it equates to the smallest cross section that can be measured point by point to verify the concentric circle around the center. For the examples below, I’m working with .308 Winchester ammo.

Concentricity run-out cartridge case
Figure 1: The cartridge.

Concentricity run-out cartridge case
Figure 2: Centerline axis of the case, extending from flash hole to case mouth.

The case walls have to be in perfect alignment with the center, or axis, of that case, even if it’s measured at a thousandth of an inch per segment (in a tapered case).

Concentricity run-out cartridge case
Figure 3: Case body in alignment with its axis, or centerline, even in a tapered case.

The case neck must also be in alignment with its axis. By not doing so you can have erratic bullet entry into the bore. The case neck wall itself should be as uniform as possible in alignment and in thickness (see the M80 7.62x51mm NATO cartridge in Figure 5) and brass can change its alignment and shape. It’s why we expand the case neck or while some folks ream the inside of the neck and then turn the outside for consistent thickness, which affects the tension on the bullet when seated.

Concentricity run-out cartridge case
Figure 4: Neck in alignment with center of the case axis.

Concentricity run-out cartridge case
Figure 5: Variations in case neck wall thickness, especially on some military brass, can cause an offset of the bullet in its alignment. This is an M80 ball round. Note the distinct difference of the neck walls.

Having a ball micrometer on hand helps, especially with military brass like 7.62x51mm in a semi-auto rifle, where there are limits as to how thin you want the neck walls to be. In the case of 7.62 ball brass you want to keep the wall to .0145″.

Concentricity run-out cartridge case
Figure 6: A ball micrometer like this RCBS tool (#100-010-268) can measure case neck thickness.

Turning the outside of the neck wall is important with .308 military cases regardless of whether you expand or ream the neck walls. There are several outside neck turning tools from Forster, Hornady, Sinclair, and others. I’ve been using classic Forster case trimming (#100-203-301) and neck turning (#749-012-890) tools for 40 years.

Bullet Run-Out
The cartridge, after being loaded, still needs to be in alignment with the center of the case axis. Figure 7 shows a bad example of this, a round of M80 ball. A tilted bullet is measured for what’s known as bullet “run-out”.

Concentricity run-out cartridge case
Figure 7: An M80 round with the bullet tilted and not aligned with the axis. This will be a flyer!

Run-out can be affected by several things: (1) improperly indexing your case while sizing, which includes not using the proper shell holder, especially while using a normal expander ball on the sizing die (it also can stretch the brass). (2) The head of a turret press can flex; and (3) improper or sloppy bullet seating. This is also relevant when it comes to using a progressive press when trying to load accuracy ammo.

Mid Tompkins came up with a simple solution for better bullet seating years ago. Seat your bullet half way into the case, back off the seater die and rotate the case 180 degrees before you finish seating the bullet. It cuts down on run-out problems, especially with military brass. You also want to gently ream the inside of the neck mouth to keep from having any brass mar the surface of the bullet jacket and make proper seating easier. A tilted bullet often means a flyer.

Concentricity run-out cartridge case
Figure 8: Proper alignment from the center of the case head to the tip of the bullet.

CLICK HERE to READ FULL ARTICLE With More Photos and Tips


*Actually some folks would say that if we are talking about things being off-center or out-of-round, we are actually talking about “eccentricity”. But the tools we use are called “Concentricity Gauges” and Concentricity is the term most commonly used when discussing this subject.

Story Tip from EdLongrange. We welcome reader submissions.
Permalink - Articles, Bullets, Brass, Ammo, Reloading 4 Comments »
May 29th, 2015

Bullet Concentricity and Related Issues

Sinclair concentricity 101 eccentricity run-out reloading plans

Sinclair International reloading toolsSinclair International has released an interesting article about Case Concentricity* and bullet “run-out”. This instructional article by Bob Kohl explains the reasons brass can exhibit poor concentricity, and why high bullet run-out can be detrimental to accuracy.

Concentricity, Bullet Alignment, and Accuracy by Bob Kohl
The purpose of loading your own ammo is to minimize all the variables that can affect accuracy and can be controlled with proper and conscientious handloading. Concentricity and bullet run-out are important when you’re loading for accuracy. Ideally, it’s important to strive to make each round the same as the one before it and the one after it. It’s a simple issue of uniformity.

(more…)

Permalink - Articles, Reloading 5 Comments »
February 15th, 2015

Bill Goad Concentricity Gauge Works by Impact

Over the years, many different concentricity tools have been on the market. Various approaches have been taken to straightening rounds that exhibit poor concentricity. With extreme examples of excessive run-out, the bullet is is visibly crooked in the neck with the bullet tip clearly off-center. That’s never a good thing. Straight ammo shoots better.

Bill  Goad Extreme Precision Concentricity  Gauge Tool Video

Straighten-Up and Fly Right
If you could straighten up crooked rounds, accuracy should be improved. In the past, some tools promised more than they delivered. But now Bill Goad, a record-setting benchrest shooter, has invented a new tool that improves concentricity via an impact or “jarring” method. A vertical rod with a curved face mates with the case-neck. You spin the case to find the “high spot” of max eccentricity. Then just tap the rod a couple of times and the neck comes back onto centerline. You can then confirm the concentricity improvement with the dial indicator. Watch the video to see how this is done. Pay particular attention to times 01:25 to 01:45. The case starts at .004″ run-out (01:32). After correction (01:40) the neck shows less than .001″ (one-thousandth) run-out.

Benchrest ace Bill Goad demonstrates his innovative Fli-Right Concentricity gauge tool. It works differently than other concentricity enhancers on the market.

Bill Goad knows something about accuracy. He shot a 10-target 100/200 benchrest Combined Aggregate of 0.178″ (see video at 00:15-00:35). Bill Goad’s tool offers advantages over systems that clamp a cartridge at both ends and try to bend the case or tilt the bullet without straightening the neck. Goad’s new Fli-Right tool is available now from PremierAccuracy.com.

Goad Fli-
Right Concentricity tool gauge

Permalink Gear Review, Reloading 11 Comments »
July 25th, 2012

New Wheel-Drive Concentricity Gauge from Accuracy One

Talented tool-maker Curt Knitt has designed a better mousetrap — a new Concentricity Gauge that makes it easier than ever to get fast, repeatable results when measuring case and bullet run-out (aka “eccentricity”). The breakthrough design feature is the large-diameter wheel which spins the case. With most other concentricity gauges you must rotate the case with your finger(s). Anyone who has tried this knows that it is difficult to get a full, 360° rotation of the case without disturbing the indicator. Typically you can get two-thirds of a rotation or so, but then you have to reposition your finger to complete the rotation. Moving your finger often causes the case to jiggle or move slightly, and more often than not, the dial indicator jumps a bit, interrupting your measurement. Been there, done that.

Accuracy One Concentricity Gauge

Drive Wheel Smoothly Spins Cases for Fast, Error-Free Readouts
With the new Accuracy One Concentricity Gauge from CTK Precision, the rubber-rimmed drive wheel has a much larger diameter than any cartridge case (7:1 diameter ratio on magnums). So, when you rotate the drive wheel just a half-turn or so (using knurled knob on the wheel axis), you can easily and smoothly turn the cartridge three (or more) full rotations. The drive wheel maintains a constant, even load on the case, so the case doesn’t wobble and the dial indicator gives a continuous, un-interrupted read-out. What’s more, clever cartridge support design geometry pulls the case back against the rim stop as you engage the drive wheel. This holds the case in position laterally during measurement. Morever, this allows very fast one-handed operation. You don’t have to hold the case down with your fingers while maintaining side force against the case rim stop.

Watch Video Showing Concentricity Gauge Used with Small and Large Cartridges

Accuracy One Concentricity GaugeThe Accuracy One Concentricity Gauge works with the full range of cartridges — everything from .22LR to .50 BMG. Adjusting the tool for different-length cases is incredibly easy, because the roller blocks (case supports) are held in place by magnets. You just slide the blocks to the desired position — no tools needed! The indicator stand is also held by magnets so it can slide to any position you want along the case body or bullet. And, the indicator can be moved to the front rail and rotated 90°. This way you can measure on the inside of the case neck.

Does this new design really work? Absolutely — it works brilliantly and it’s FAST. Watch the video and see for yourself. We could do two-rotation (720°) measurements on cases in a third the time it takes to do a one-rotation gauging operation with other tools. And the actual measuring operation can be done one-handed, leaving your free hand to pic up the next case (or bullet) to be measured. And yes, this tool can also measure bullet concentricity — measured from tip, ogive, bearing surface, and/or boatail.

Accuracy One Concentricity Gauge

1. Directional Drive Wheel pushes the cartridge or bullet into the stop for accurate, repeatable readings with equal pressure. The replaceable rubber drive ring will not harm cartridges or bullets.

2. Two-position bullet and cartridge stop.

3. Precision ball bearings provide friction-free movement.

4. Heavy steel base with E-coat finish and bolt-on rubber feet.

5. Indicator stand and roller blocks ride in machined slots and are held in place by N42 Neodymium magnets. This allows rapid, smooth, tool-free adjustments.

6. Indicator stand can be place in front OR rear machined slots. This allows for both internal and external measurements.

7. Fine-Adjustment Horizontal Indicator Stand allows very precise indicator angle/load adjustments.

8. Indicator Stand will accept horizontal indicators that are .350″ wide or narrower, and are 1.75″ to 2.25″ from the indicator contact point to the center of the main body.

9. Adjustable mechanical arm stop holds the arm up for one-handed operation.

10. Precision Drive Wheel has a 13:1 ratio for .22 rimfire, 7:1 for magnums, and 3.7:1 for 50BMG.

11. Concentricity Gauge accepts cartridges from .22LR rimfire to .50 BMG.

The Accuracy One Concentricity Gauge is available from BulletTipping.com. Price for the unit, complete with quality horizontal indicator, is $325.00. Price, without indicator, is $280.00. The initial run of Concentricity Gauges is now in final production. Gauge sets should hit the market in 4 to 6 weeks. To place an advance order, fill out the PDF Order Form, or call (814) 684-5322. To learn more about setting up and using this new tool, read the Concentricity Gauge Instructions, and watch the video above.

Permalink Gear Review, New Product, Reloading 9 Comments »
December 25th, 2011

21st Century’s Impressive New Concentricity Gauge

21st Century Shooting’s all-new Concentricity Gauge looks like a winner. The cartridge case rides on four spinning rollers that allow smooth turning movement with low drag. These rollers are far superior to a set of V-Block supports, or even some ball-type supports.

The amount of eccentricity (run-out) is measured with a high-quality horizontal dial test indicator. In this application, a horizontal indicator works better than the typical vertical dial indicator with spring-loaded shaft used in most other concentricity gauges. We think that, with 21st Century’s new Concentricity Gauge, you can measure cases faster, with less effort, and greater repeatability. In addition, this device can measure the INSIDE of the case neck, not just the OUTSIDE.

Overall, this is a very impressive new tool that is unquestionably superior to many other Concentricity Gauges on the market. Given the capabilities of this device, the price is reasonable: $169.00 including Horizontal Indicator. The Gauge by itself costs $125.00, while the Indicator alone sells for $59.00.

Click Photos below to view larger Images

Why the New 21st Century Concentricity Gauge Works So Well
21st Century explains the advantages of its new design: “At 21st Century Shooting, our goal to modernize an industry that has seen little change over the years. The new concentricity gauge is a perfect example. Most conventional concentricity gauges use what is called a height indicator gauge (Dial Indicator with vertical shaft). Although economical, this type of gauge was not intended for the purpose of measuring rotating diameters. The vertical-style indicator can produce inaccuracies due to indicator rod flex and bounce.

Our new Concentricity Gauge uses a horizontal dial test indicator. This type of gauge was designed specifically for checking rotating diameters and in fact is exactly the type of gauge used in the machining industry for decades to measure run out — the very thing that we as hand loaders are striving to minimize or eliminate.

Additionally, our new gauge uses Stainless Steel turning rollers as opposed to fixed bearings or V-block style case supports. You will especially appreciate the roller supports that glide on linear guide-ways. Plus, with a simple push of a button you can adjust the case support base width. No tools are needed to move the base on the built-in guide-ways.”

Product tip from EdLongrange. We welcome reader submissions.
Permalink Gear Review, New Product, Reloading 5 Comments »