Hi everyone,
I've been a long time lurker and I'm hoping the community might be able to help me out.
I purchased quickload to assist with developing loads and now I'm stuck overthinking the water case capacity input. When I input this weight, do I include the case capacity WITH the primer or should I subtract the weight of the primer to get the true weight of the empty brass? Any input would be appreciated!
The idea is to obtain the water weight equal to the filled internal volume of a case that has been fired and expanded to fit the chamber. That water weight can then be directly converted to volume because for all practical purposes, one milliliter of water = one cubic centimeter of water = one gram water weight. Whether you write down the empty/full case weights and subtract, or use the tare (zero) feature and let the balance do the work for you doesn't really matter, as long as you end up with the exact water weight/volume of the fired case.
The reason QuickLoad software suggests using a case that has been fired but not re-sized is that it best represents the total pressure cell volume for the chemical reaction that takes place when a round is fired. The amount of energy required to expand the case and move the shoulder forward in
virgin brass is not zero, but it is not a very large fraction of the total energy, either. In my hands, a load in fire-formed brass typically requires about 0.1 to 0.2 gr less powder to achieve the same velocity as with virgin brass.
We typically move the shoulder of fire-formed brass back only .001" to .002" and squeeze the sides down just enough that the re-sized case can be chambered without difficulty. The elasticity of brass allows it to contract very slightly (i.e. spring-back) so that it can be extracted from the chamber easily. Nonetheless, fire-formed brass is expanded relative to re-sized brass, and its volume is therefore even closer to the true pressure cell volume. It may not be "perfect", but it would take well under 0.1 gr powder in most cases to produce the energy required to expand fully fire-formed brass that tiny little bit more. In other words, the effect of the volume difference between fire-formed brass and fully expanded brass (i.e. in the chamber during firing) on QuickLoad outputs is negligible.
We measure velocity and groups as useful readouts during load development, which are events that occur long after the brass has expanded to perfectly fit the chamber, then contracted. As long as the contracted (i.e. fire-formed) brass is consistent, it is the most accurate representation for the pressure cell volume that we can readily measure. In my hands, the external dimensions of fire-formed cases are extremely uniform and the [average] fire-formed case water volume works very well as an input for QuickLoad. Of course, QuickLoad users are free to use whatever volume input they wish. However, as I described above, there is a very good reason the manufacturers of QuickLoad recommend using the water volume of fire-formed brass, rather than virgin or re-sized brass.
