Reloading for Concentric Cartridges

by Admin | Last Updated: June 10, 2020

To ensure the best possible hand loaded cartridges and ammo, it is necessary to follow a longer process.

People who practice the hobby of hand loading or reloading of ammunition often find that their loaded cartridges are not very concentric.

If you test the total cartridge on a run-out gauge, you will see the bullet wobble in the case. This means that the bullet was not pressed straight into the case or that the case itself was skew, thus causing a skewed cartridge. Usually, such skewed cartridges ruin a loaded lot of ammunition and the rifle’s accuracy potential, as well as hamper your load development results and process.

run out gauge

A skewed bullet is unstable when it leaves the case and unfortunately it is not straightened or stabilized through the barrel. Leaving the barrel it is usually still unstable. Some people believe you can push a bullet straight that is loaded skew into the case (there are even devices for this purpose) but when it does, the case’s neck tension on the bullet becomes looser. This in turn causes varying neck tension from cartridge to cartridge which causes variations in bullet speed and pressure levels and adversely affects accuracy.

So the secret is to always start with a concentric or straight case. When buying new cases, you will always find a few of each box that are curved or skew. Some people just keep them aside for use only for practice on the shooting range. But actually, casings must first be fired in your rifles’s chamber and then you can judge and class them again.

If the chamber is properly machined and there was no fault with the reamer, fired cases will always be straight (including the body and neck alignment) when they come out of the chamber – measure them. Those that were skewed were due to reasons other than a skewed chamber.

Don’t Resize Unnecessarily

The reamer with which the chamber is machined simultaneously cuts the whole chamber which includes the body, shoulder, neck and often also the free bore and throat. The likelihood that the parts of the reamer are skewed or manufactured out of alignment are very slim. Fired cases take the shape of your rifle chamber and fit snugly into it, this is called fire forming.

Therefore their dimensions only need to be changed or altered as little as possible, because excessive resizing can make them crooked. If the case is resized to such an extent that it fits loosely in your rifle’s chamber, even a straight pressed cartridge can be skew in the chamber, adversely affecting accuracy.

My experience is that most full length sizing dies, excessively resize the cases and therefore causes some skewing in them. The specifications according to which all factory rifle chambers are(or should be) manufactured, are in accordance with the Sporting Arms and Ammunition Manufacturers Institute (SAAMI) specifications. SAAMI regulates that for each specific caliber there is a minimum size for the chamber and a maximum size for the ammunition. This will allow all ammunition for a specific caliber, regardless of the brand, to fit into the rifles of any other manufacturer and operate safely. Therefore, there is usually a very loose fit between a factory rifle’s chamber and factory ammunition.

Full length sizing dies are also manufactured to the SAAMI specifications. These dies must cater for all manufacturers’ cases, some of which’ wall and neck thicknesses can often differ greatly from one another. The result is that these dies resize the cases a lot more than is necessary so that the ammunition can fit into all rifle’s chambers.

There is also another disadvantage if cases are resized too greatly. Brass hardens when repeatedly worked. Therefore, excessive resizing also leads to a shortened lifespan of the casings. The process of excessive resizing can be controlled, but more about this later.

Skew Necks

When full length sizing die are used, they over tighten the neck of the case and the expander ball then pulls it open again to the correct inside diameter. Unfortunately, this action often causes the necks of the cases to be skewed, as so we do not recommend a normal full length sizing die as the best dies for precision reloading. The expander ball is usually part of and attached to a sturdy steel pin. Here, the pin is also tightly fastened to the die and its alignment is sometimes not straight. The cases also fit loosely into the case holder. Therefore, when the expander ball is pulled through the case, a combination of the above causes a lot of strain is placed on the neck and can bend it to one side or the other.

In extreme cases, the part where the case neck and shoulder join together can be stretched so that the case fits very tight into the chamber. Then, the bolt locking pins then push the shoulder back the required amount so that the bolt can close. This causes wear of the locking pins and, in my opinion, can be detrimental to the head space of the rifle.

A type of die is available that only resizes case body and shoulder, without touching the neck. It is called a body die, Redding manufactures a good one. You can also have your own body die made by getting the top part of a full length sizing die machined off. After using the body die, the neck is then resized with a different die.

You get regular neck sizing dies, but they all have expander balls that can skew the neck. Of the dies that do not have expander balls, there are two common types, namely Lee’s collet die or Redding bushing neck sizing dies. Both work well and each has its own way of doing things.

Lee Collet Neck Sizing Die

Lee’s collet dies presses the neck around a steel pin and releases the case neck once the press is released. The thickness of this pin controls the neck’s inner diameter. So there is no expander ball forced through the neck to pull it open (and very often skewed). The only way to change the inner diameter of the neck is to change the diameter of the pin. Here the die works great and is much cheaper than the bushing neck sizing die.

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Redding Bushing Neck Sizing Die

With the Redding bushing neck sizing die, there are different sizes of bushings or bushes that can be replaced so the neck is resized to the desired amount. The sizes of the bushings differ in steps of one-thousandth of an inch (1 Thou). So for each different neck diameter you need a separate bushing. The cost of these dies and bushings is much more but the Nitride bushes also do not require case lube to be used for resizing, and they would for sure be one of the best dies for precision reloading in our opinion.

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Correctly resizing the case is the most important step in the reloading process.

Method

  1. First, the cases are cleaned. By tumbling cases, they are made shiny and clean on the outside, but rarely inside. Often an abrasive is added to the media to aid the process. Some of these abrasives can get stuck on the inside of the case and stay behind. When the shot is fired, some of this abrasive substance may end up in the barrel and the next bullet will shoot over it. Maybe something to think about. Chemical processes and ultrasonic cleaners are probably safer and also clean the inside.
  2. Then I measure the diameter of the fired case’s neck and shoulder as shown in the sketch. Preferably take these measurements with a micrometer. Usually, about five measurements are taken in various places on the circumference of the case to have starting measurements. It can also be measured with a caliper vernier. Measure the head space as shown (see sketch) with a vernier and a comparator. You will use these measurements later.
  3. Then I remove the primer without resizing the case. Redding’s universal decapping die can be used for this. Some other dies, such as the Lee collet die, can also be setup for decapping. Press the Lee collet die in until it just touches the case holder. Now loosen the Lee collet die one full turn. This will only remove the primer and not resize the cas at all. Due to the pressure during the firing of the shot, the primer can sometimes protrude slightly behind the case head. This then causes you to take a wrong measurement of the headspace. With the primer removed, the primer pocket can also be cleaned in step 2.
  4. If necessary I anneal out the cases.
  5. Suppose you use Redding’s body die then it must be set up. Remember, this is done only once (before you start reloading) for each caliber / case combination. Engage the press so the shaft is at the top. Set the body die so it touches against the case holder and create a reference mark on the die’s top with a permanent marker. Unscrew the die a ½ turn.
  6. Apply a thin layer of lubricant to the case body and shoulder. Size the body and shoulder in the body die.
  7. To size the case just enough for a comfortable fit, reduce the size of the case by about one-thousandth of an inch (1 Thou). It is about 0.03mm. The two measures that will make the difference here are the measurement for both the diameter of the shoulder and the length of the head space. The one that changes the least is decisive. The other measurement may reduce by more than one-thousandth of an inch (1 Thou).
  8. Measure and compare the dimensions of the resized casing with those measured in Point 2 above. If necessary, set the body die about 1/16 of a turn deeper and repeat the sizing and measuring process. Keep going until both the shoulder diameter and head space have been reduced by at least one thousandth of an inch (1 Thou).
  9. Feel the resistance with which the rifle bolt closes without anything in the chamber. Carefully chamber the sized case above and confirm that there isn’t much more resistance to closing the bolt than with the empty chamber.
  10. The casing neck can now be resized. Usually the neck diameter expands a total of about two thousandths of an inch (2 Thou) after the bullet is pressed in or seated.
  11. Use a Lee’s collet die or a Redding bushing neck sizing die, make sure to use the best dies for precision reloading. Adjust the dies and repeat the process until the neck diameter expands to the desired two-thousandths of an inch (2 Thou) after the bullet is seated. Make notes of the setting on the dies when reaching the correct amount of case sizing so that you can repeat it later if the dies are reset or change for some reason. The acceptable amount of misalignment for a loaded cartridge which is very good is below 2 Thou, up to 4 Thou is acceptable, but more than that is considered good enough for distances up to 100m. What is described above may sound like extra work, but this longer process is essential to ensure the best possible hand loaded cartridges.

Another important point to remember is the use of a good single stage reloading press, often it is at this stage of pressing the bullet into the case, that it can be pressed in skew or at an angle if the press allows that. A well designed and machined press will prevent that from happening. Just as a matter of good practice, I always just turn the whole cartridge 108 degree in the shell holder after seating a bullet, and then press it again, just to ensure any further concentric alignment in the seating.

Now as always, get out there and shoot shoot shoot!