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 »
November 13th, 2012

Get 10% Off All 21st Century Tools and Reloading Products

21st Century Shooting crafts some of the best precision handloading tools you can buy. This company’s neck-turning tools, priming tools, funnels, flash-hole tools, and other specialty tools are truly excellent pieces of kit. The 21st Century neck-turner, fitted in the company’s innovative neck-turning lathe, is an outstanding system for turning case-necks. Now holiday shoppers can save money on 21st Century’s entire product line. 21st Century is offering 10% off all products ordered through its website, www.21stCenturyShooting.com.

To get 10% off your online order, simply use the Discount Code 1210holiday25 during check-out, placing “1210holiday25″ in the box marked “REDEEM CODE”. With the money you save you can buy more cool tools, or set aside your savings for bullets, brass, and powder.

21st Century Shooting Concentricity Gauge

Discount Tip from EdLongrange. We welcome reader submissions.
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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 »
January 14th, 2012

Videos Show Functions of Hornady Concentricity Gauge

UltimateReloader.com created an informative video that shows how to use the new Hornady Lock-N-Load Concentricity Gauge and Ammo Straightener. This tool can measure run-out on both the bullet and on the case-necks. Run-out is deviation from the cartridge centerline axis. Too much run-out, i.e. poor concentricity, can reduce accuracy, although when you seat bullets into the lands, a certain amount of bullet self-straightening can take place.

Hornady Concentricity Gauge

Hornady Tool Supports Cartridge on Both Ends
The new Hornady Concentricity Tool supports the case at two ends. As a result, the Hornady Tool will tend to yield lower run-out figures than a tool such as the Sinclair concentricity checker which supports the cartridge on the case body alone, giving the bullet unrestricted movement as the case body is rotated. As UltimateReloader explains: “Each measurement tool measures run-out differently, so you’ll need to factor that into your goals for your own match ammunition.”

YouTube Preview Image

Bullet ‘Straightening’ with Hornady Concentricity Tool
The Hornady Tool can be used to push seated bullets to one side or the other, reducing measured run-out. The Hornady tool has a threaded pusher that side-loads the bullet. As you screw the pusher inwards in you can see the run-out on the dial indicator decrease. That straightening process is shown in the Hornady-produced video below, at the 25-second mark. In Sinclair Intl’s Reloading Press blog, Pete Petros reports: “It can take a little bit of trial and error to get this just right, but it does work.”

YouTube Preview Image

Is Bullet Straightening Really That Effective?
This bullet straightening procedure, whether done with the Hornady tool or other device, is a somewhat controversial technique. Some folks say that straightening bullets simply transfers run-out back down to the case neck. Petros notes: “One concern that comes up is what are you doing to the neck of the case in terms of neck tension.”

On the other hand, many shooters claim their ammo shoots better after they straightened rounds which initially showed excessive run-out. One Hornady Concentricity Tool user writes: “The straightening feature on the Hornady tool makes bullet/case concentricity easy to correct and after using this tool, I wouldn’t be without one. Variations on [my] cast bullets have gone .020″ and when straightened, I can get down to below .001″. It takes a bit of practice, but it’s possible to make every round straight. At the 100-yard range yesterday using my straightened rounds … five-shot groups averaged .500. Before I would always have flyers and now I can see why this time I didn’t have any flyers. Straight rounds produce more consistent groups!”. Read more.

Bullet straightening with the Hornady Tool or other devices can certainly make a difference in run-out that shows up on the dial. Whether that improvement in perceived concentricity actually produces better accuracy remains an open question. Using high-quality dies with good bullets, seated in good, straight brass, you should be able to load ammo with very low run-out from the get-go. It may be better to try to achieve low run-out during your normal loading process rather than rely on the “band-aid” of bullet straightening as a last resort. On the other hand, if you are starting with factory-loaded ammo, re-aligning bullets in the case-necks may be a useful exercise. We invite our readers to comment on their experiences with bullet straightening. Has the straightening process worked for you?

Permalink - Videos, Gear Review 7 Comments »
August 12th, 2011

Big Sale on Hornady Reloading Products at Grafs.com

Grafs.com is having a big sale on certain Hornady reloading products. The Lock N Load Auto Charge Scale/Powder Dispenser is now just $199.99, marked down from $224.99. Reports on this unit have been generally positive. This sale makes the Hornady scale/dispenser much less expensive than an RCBS Chargemaster, which typically sells for about $330.00.

Hornady Auto charge Dispenser Scale

Next, the price of the Hornady Lock N Load Ultrasonic Cleaning Machine has been knocked down to $84.99 from $99.99. That makes the machine cheaper than “no-name” alternatives sold on eBay. This is similar to the machine we used for our original ultrasonic cleaning tests. It should do the job, unless you have large quantities of brass, in which case we recommend the larger Hornady Magnum Sonic Cleaning Machine, which has twin transducers and a larger immersion bay.

Hornady Ultrasonic Cases Cleaner machine

Grafs.com has also slashed the price of the Hornady Concentricity Gauge from $94.99 to $79.99. This tool can measure bullet run-out, and it has the capacity to straighten bullet alignment in the neck. Be aware, however, that because this tool supports a cartridge at both ends (like holding the two ends of a jump-rope), you will typically get a different run-out reading than with a traditional tool, such as the Sinclair Concentricity Gauge, which supports the case body only (without touching the bullet tip). Both tool designs give meaningful results, but the read-outs will not normally be the same.

Hornady Concentricity Gauge

Hornady reloading manualHornady Reloading Handbook $10.00 with Bullet Purchase
In addition to the tool sales, Grafs.com is now offering the lastest Hornady Reloading Handbook for just $10.00 if you purchase five (5) boxes of in-stock Hornady Bullets. If you could use the book, we recommend Hornady’s V-Max bullets for varmint hunters, and the new BTHP match bullets for target shooters. The new BTHP match bullets feature AMP (Advanced Manufacturing Process) jackets for greater dimensional uniformity.

Permalink Hot Deals, Reloading No Comments »
October 5th, 2010

H&H Concentricity Gauge and Bullet Straightener

In our feature article on Case Neck Tools we explained the importance of case neck uniformity and reviewed the best tools for measuring case neck thickness. But having uniform case neck walls is only part of the accuracy equation. You also want your cases to exhibit minimal run-out, as measured by a precision tool. For this reason, a quality concentricity gauge belongs on your loading bench if you are looking for the Nth degree of accuracy.

We’ve worked with quite a few concentricity gauges. They all have their strengths and weaknesses, but some just didn’t perform well at all with very short cases like the 6BR and 6PPC. One of our regular readers suggested we check out the H&H Concentricity Gauge, made by Bill Herron in Oregon. So far we are very impressed. A 6BR or PPC case doesn’t tip or rock, causing the needle to jump. We were able to get good, repeatable readings off a seated bullet, which wasn’t easy at all with some of the other units. Our friend agreed with our positive assessment of the H&H, saying: “I have four concentricity gauges. Among these tools, the H&H is the least expensive and the easiest to use of those designed for loaded round measurement AND bullet straightening. It is also built like a brick. However, the Sinclair is [probably] the best for looking at the case alone due to the bearing balls and their adjustability.”

The H&H uses an indicator block to eliminate off-center indicator readings. It will accept .22 PPC through .375 length cases. A reversible spindle acts as a pilot for checking neck thickness. Bill Herron says the unit can also re-align bullets, but we didn’t try out that capability. For more info, visit the H&H Industries website, or call Bill at (541) 327-1411.

H&H concentricity gauge

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