Reloading Basics: Switching Brass Brands & Impact on Loads

Reloaders all tend to have a favourite ‘pet’ load for each calibre, and they stick with it most of the time, but occasionally a shortage of components can force a change. When it comes to the brass that you are using, having to switch to a different brand can have a very significant effect on your preferred load.

How Do External vs. Internal Case Dimensions Differ?

The external dimensions of cases tend to vary very little from brand to brand, with almost all cases being made to SAAMI standard dimensions. It is only manufacturing tolerances that might mean that dimensions vary by a fraction of a thousandth of an inch here and there between brands. If you full-length resize all of your cases, including new cases, before you use them for the first time, this will standardise the outside in line with the dimensions of your particular die.

The internal dimensions, and therefore the volume, of different brands of cases can vary significantly, and this can have a big effect on how your ammunition performs. The thickness of the brass in the case walls varies a lot from brand to brand, with the more expensive brands usually having thicker brass, and the thicker the case walls are, the less volume there is inside the cases for the powder and the combustion. If a given powder charge is confined to a smaller space when it ignites, the chamber pressure generated will be increased. When you are using a near-maximum load and you change to cases with a lower internal volume, it is possible that you will push the chamber pressure to a dangerous level.

When you change the brand of cases you use, it is a good idea to check and compare their internal volumes. The easiest way to do this is to completely fill a case with water, so there is a curved bulge of water under surface tension at the case mouth, and weigh it. Then do the same with the other brand. A gram of water occupies one cubic millilitre, making it very easy to compare volumes. Some reloading software, such as QuickLOAD, allows you to input the case capacity (in grains of water or cubic centimetres) and then recalculate muzzle velocity and chamber pressure, which is really useful if you are using cases from different manufacturers.

If the new cases have a smaller internal capacity than the ones you have been using, you will need to reduce the powder charge slightly to achieve the same muzzle velocity and chamber pressure. While it is not possible to measure the chamber pressure easily, it is relatively easy to check muzzle velocity, and this is a good indicator of any changes in chamber pressure. The powder charge will only need to be adjusted by a couple of tenths of a grain, and a bit of experimentation will be needed to duplicate the muzzle velocity of your pet load.

If the new cases have a larger internal capacity, then you will have to increase the powder charge slightly to achieve the same muzzle velocity. Again, just a tenth or two of a grain adjustment should be all that you need.

Why is Neck Tension Important When Changing Brass?

Different case manufacturers use different metals, of different thicknesses, and apply different heat treatments to them, so the way that the metals behave can vary significantly. Nowhere is this variance more important than at the neck of the case, where it engages with the bullet.

If the metal is thicker, and the outside dimension of the brass at the case mouth is the same, then the brass will naturally grip the bullet tighter, as the inside diameter will be smaller. When you are resizing cases, the case neck area is resized, which dictates the amount of neck tension, and the amount of tension will vary depending on the thickness of the brass.

In a situation where you find that the brass at the mouth of the new cases is 0.0005” thicker than that of the previous brand you were using, they will produce neck tension that is 0.001” (2 x 0.0005”) tighter in the same die, if it is not adjusted or changed. With dies that utilise neck sizing collets of different diameters, you can vary the amount of tension you achieve and cancel out the effects of the different brass thicknesses. In the above situation, you could simply change the neck sizing collet to one that is 0.001” larger, and this will accommodate the thicker brass and keep the neck tension similar. Due to other factors, such as heat treatment and the composition of the brass, it is unlikely that the neck tension will be exactly the same.

New brass cases are typically annealed, particularly in the neck and shoulder area, to prevent cracking or splitting during either firing or reloading. The method and temperature used by different manufacturers will vary, and this will affect the ‘springiness’ of the metal, typically ensuring consistent neck tension within the brand, but varying between brands. The annealing process also reduces the tendency of the brass to spring back to its original size after resizing, again making it possible to achieve consistent neck tension. Although some reloaders do anneal their cases themselves to keep things as consistent as possible, most reloaders do not go to this extreme, and the differences between how cases from different brands perform due to the ways they are annealed are not realistically possible to address.

Why Do Flash Holes Vary and How Can You Uniform Them?

Another area where cases from different brands can vary is the size of the flash hole, and this can also be significant. Most are formed to a standard size, but some brands have slightly smaller or slightly larger flash holes. Variations in flash hole size can affect how consistently the primer ignites the powder charge, which will directly affect accuracy and chamber pressure. This can be addressed by uniforming the flash holes, making them all the same size and shape. Specialised flash hole uniforming tools are readily available and can be a worthwhile addition to the reloading bench.

Conclusion: Managing the Impact of Changing Brass

Although not ideal, if you find that your usual supply of cases dries up, and you are forced to buy another brand, you can manage a lot of the impact it has on your reloads. The case capacity and brass thickness are significant, but can be counteracted to a large degree, and the flash holes are easily standardised.