Of Case Capacities, Bulk Densities, and Accurate Predictions

[gitano]

One thing folks can do to get a feel for how variance in measurement of case volume affects the output in QL is simply to set up a specific load in the program, then vary the case volume incrementally in either direction and see how the predictions change. This is a useful exercise not only getting a feel for how different parameters in the the program work, but also to get some idea of how much minor variance in different measurements will affect the outputs. If you already have the program, it doesn't cost anything but a little time.

I should also add that in my hands, burn rates can change dramatically for the exact same lot of powder in different cartridges. YMMV, but as an example, the Ba for the same lot of H4895 in .223 loads and .308 loads is noticeably different. For the same reason, the factory preset burn rates vary quite a bit for a given powder depending on the cartridge. They will be much better for some cartridges, farther off for others. Because of that I always "calibrate" a lot of powder in a specific cartridge with a specific bullet, brass, and primer, at a charge weight reduced by a few percent from the OBT load predicted using the preset factory burn rate. Note that the predicted OBT nodes are generally under MAX pressure to begin with, I'm just adding a little more headroom for safety reasons. The caveat is that depending on how far you need to go up in charge weight to reach the node, you will likely have to tweak the burn rate again to get predicted MV to match actual MV. As pressure goes up, so does the burn rate, therefore Ba will likely change as you increase charge weight.

I couldn't have said it better nor would I change a word.

I'll have to look up the site I saw for Bromel's stuff.

Paul