The straight and narrow: Byron Pace evaluates loaded ammunition with the Hornady concentricity gauge

01 Hornady concentricity gauge1

After 12 instalments of this series on reloading, we finally have loaded ammunition that shoots where we want it (yes, it’s hard to believe we have reached an entire year of reloading). If this is the case, then there probably isn’t anything particularly wrong with your ammunition and, for the purposes of the majority of hunting, this series could terminate here. There is a limit to just how ‘accurate’ we need our ammunition to be. Having said that, rifle shooters are a funny bunch, and for most there is a never-ending drive towards better or different loads. For that reason, I will continue.

It may also be the case that, despite your best efforts, the ammo just won’t shoot. In this case we need to start looking at what went wrong. It is very unlikely at this point that your ammunition will be all over the place. It may not be as tight as you would like, but it should still shoot something resembling a group. The issue could of course be the rifle, and a quick check for this is to see how a few rounds of factory ammunition run through it. There may, however, have been some errors in the reloading process itself.

Dialled in: A concentricity gauge can tell you a lot

Dialled in: A concentricity gauge can tell you a lot

One aspect which can make a big difference to how well your ammunition shoots is the concentricity of the loaded bullet. By this I mean how straight the bullet is loaded into the case mouth. This is important because we want the bullet to leave the case as straight as possible, with the ogive meeting the lands of the rifling uniformly. A bullet which is canted to one side will slam into the rifling at an off angle, doing the accuracy of your load no favours at all. Of course, we are talking very small variances, in the region of a fraction of an inch, but it can make a big difference, especially at extended range. From my experience, factory ammo is very good at achieving low run-outs. Testing Hornady Superformance ammo gave just a 0.0015in average run-out, with Sako also showing tight tolerances. Turning to some of the budget ammo revealed bigger variances, with Sellier and Bellot coming in around the 0.006in run-out.

Extreme case: A factory cartridge with major issues

Extreme case: A factory cartridge with major issues

More seriously, I recently removed from a box of ammo a round that was totally off centre – this was however due to deformity of the case neck as opposed to the bullet being loaded incorrectly. This could of course also be an issue in reloading and we will examine this.

Normally, you wouldn’t be able to tell by looking at the loaded bullet if it was concentric or not. One crude test is to lay the loaded cartridge on a table and roll it with the bullet point facing you. Watching at eye level, in more severe cases it is possible to see the bullet point rotating unevenly with the centre of the case mouth. This is a lot easier to see with sharply pointed bullets, such as those with polymer tips.

There are a number of devices out there that let you check the concentricity of your bullets, and as always some are better than others. One gripe I had with my Forster Co-Ax was that it marked the bullet on rotation. Once you are confident in your reloading process there shouldn’t be a need to check every bullet, and a half decent bullet seater, set up correctly, should achieve a consistent result – assuming the brass sizing process hasn’t caused an issue. Checking one in every ten bullets is more than enough, and having used my own set up for so long now it is only periodically that I bother. If everything isn’t going to plan then it is a necessary check.

The small cone accepts the bullet

The small cone accepts the bullet

The difference between a bullet being seated perfectly and sitting off centre is called the ‘run-out’ of the bullet, and ideally should be 0.004in or less in a hunting cartridge. For long range shooters 0.002in or less is normally desired. Don’t expect your loaded ammo to be perfect: it is very unlikely you will be able to load your ammo to have zero run-out, and even top-notch bench rest loaders accept a small amount. If you can reach 0.002in run-out you are doing very well.

Until recent years there hasn’t really been a way to correct for bullet run-out, apart from evaluating the whole process and improving each step. This is still the best option if you are finding excessive run-out on loaded ammo, as fundamentally something must be wrong.

The large cone centres the cartridge head

The large cone centres the cartridge head

Hornady offer a tool that allow run-out to be corrected at the same time as checking for concentricity. The Lock-n-Load concentricity tool uses two sliding rods to hold the cartridge, each machined with a cone on the inside face. The wider of the two houses the head of the cartridge, fixed into position with a large tensioning wheel at the front. At the opposite side a small cone under tension accepts the point of the loaded bullet. With the bullet supported evenly at either end, rotating it will expose any eccentricity between the two components. By setting the dial nib about half way along the bullet shaft, then zeroing the face, rotation will cause the dial to fluctuate above and below the start point. Adding any of the values together will give you the run out (i.e. if you get -0.002in as the lowest reading and 0.006in as the highest reading then the run-out is 0.008in). As long as it’s set correctly, without too much tension, it shouldn’t damage the bullet.

One aspect which can make a big difference to how well your ammunition shoots is the concentricity of the loaded bullet

Having established which face has the minimum run-out (producing a negative reading, or the minimum reading you achieve), steady the bullet while screwing in the setting screw on the side of the cradle. When the protective tip touches the bullet, tighten up a little further and then back off. Rotate the bullet and check again. This should have reduced the run-out by pressing against the edge of the bullet that leans towards the outside of the case. If run-out still occurs, repeat the process gradually until the dial barely moves from its starting position.

Some gauges mark the  bullet after testing

Some gauges mark the bullet after testing

I have to admit this is not a facility I use, instead optimising my loading to minimise run-out in the first place. I’m happy to leave a standard 0.001 inch in my process: I don’t think it makes any difference for a hunting load, and it’s far too time-consuming to fix every bullet. As I said before, if you are suffering from severe eccentricity, you need to establish why.

Some gauges also allow you to check if the outside of the case neck is concentric. Usually, but not always, the last part of the sizing process is completed on the inside of the case neck, meaning this should be uniform and any differences are pushed to the outside. We are essentially looking at any difference in the neck wall thickness. In standard hunting chambers this is probably not going to cause any issues, and I can’t say I have ever seen quality brass show anything to cause concern. We are not going to get into neck turning for making hunting ammo – we will leave that to bench rest shooters.  If you do want to check, you can purchase the additional bolt-on Neck Wall Thickness Gauge kit.

Now we have the measurements out the way, we can go through pitfalls and corrections.

Poor trimming can lead to eccentric loading

Poor trimming can lead to eccentric loading

Case preparation

The first check is a simple one. Make sure your case trimming tool is cutting a square face on the mouth. Canted to one side, it will not only lead to eccentric bullet seating, it will also give inconsistent neck tension – a vitally important component of producing accurate ammunition. Following on from trimming, careful inside de-burring is also important. It prevents sharp brass edges damaging the bullet, while also stopping folds of burrs being pushed back into the neck on loading a bullet, which will affect how much the brass grips the bullet shank.

Variations in neck wall thickness are a pain, because there really is only one way to fix that, involving neck turning your brass. We won’t cover this, but if you are finding large variances in cheaper brass, simply bin the worst.

Bullet seating

I have to admit that a couple of years ago I was stumped by poor bullet concentricity while loading some Hornady A-Max bullets. Despite carefully checking the cases, no matter what I did the bullet would seat skewed – in a major way. Eventually I worked out that the tip of the bullet was bottoming out on the inside of my seating die. Instead of supporting the bullet around the jacket, it was wobbling around on the point. Using a seating die designed for high BC, long nosed bullets fixed this problem instantly.

We will be looking at seating dies next month, and how different types aid concentric loading. It is also important to note that your bullet must be seated at an accurate depth within the case every time. The reasons for this we have already covered.

Something that is true not only of seating but also the re-sizing process, is ensuring that you have the correct shell holder in the press. The shell holder only serves as a guide, and should not hold the case fast. What we really want is for the case to float a little so that it can self-locate in the die for the most accurate loading. One way to help improve this is to remove the locating spring clip on your press and replace it with a rubber o-ring. This allows the shell holder to float.

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