Add a new powder from your own measurements

You can make a propellant model for your own use directly in the program. The model values (Ba, a0, z1, z2) are fitted to your chronograph data. The result is saved as an own record, so you can use the powder in every load. (To contribute a powder to the project database, see Procedure 2.)

CAUTION: Reloading is dangerous. Use only loads from the current load data of the manufacturer, and start low. The result is only as good as the measurements and the data of the powder.

What you need: a chronograph (for example MagnetoSpeed or Labradar) and, if you can, a pressure measurement. The more different loads you measure (2 or more calibers, 2 or more bullet weights, 2 or more charges each, at least 5 shots per charge), the better the model fits other loads. One load with few charges only determines Ba.

  1. Start from a similar powder. Open the tab Database, select the Propellants list, select a powder with a similar burn rate and click Copy…. (Or click New… if you know all values.) Type the name, the manufacturer and the lot. Check the values that you know: explosion heat Qex, ratio of specific heats k, material density pc, bulk density pcd and the reference temperature pt. These do not come from the fit. Optionally add an overview photo and a detail photo (Choose file…, with the scale in px/mm if you know it). Click Save.
  2. Make a load with the new powder. Create a load with File ▸ New load… (or open a .csrload or .grtload file). On the tab Propellant click Select Propellant… and choose your new powder.
  3. Measure the case and the cartridge. Measure the volume of a fired case with water and type it into Case Volume. Measure the length of the bullets and the cartridges and type the mean values into Projectile Overall Length and Cartridge Overall Length. A good case volume makes the fit much better.
  4. Type the measurements. Open the tab Measurements. Click Add charge for each charge (or Add ladder charges). Select a charge and type the velocity of each shot in the shot list (and the pressure, if you measured it). You can also use Paste shots (one shot per line, velocity and optionally pressure), or click Import chronograph file… and choose a Garmin Xero .fit (or the CSV of the Xero app), a MagnetoSpeed .csv or a Labradar Report.csv. The files do not contain the powder charge: type it for each series in the import dialog. The table shows the mean velocity, SD and ES and the difference to the simulation. Use New series if you have several measurement series for the load (for example one for each range day).
  5. Fit the model. Click Fit to measurements…. Check which values to fit (the default depends on the data: Ba alone for fewer than 3 measured charges, Ba and a0 for 3 to 5, all four values for 6 or more charges from at least 2 load files) and click Fit. The dialog shows the velocity and pressure of each charge before and after the fit. Read the warnings, for example when the case volume is only the database value or when there are fewer charges than values. With the physical model (the default) and a project powder, the fit changes the load's physical burn values (Physical Model: ... in the propellant table) and keeps them in the load; Save as own propellant… is then not offered.
  6. Check the result. The differences after the fit should be small (less than approximately 2 % in velocity). If they are not, check the measurements, the case volume and the bullet and powder data.
  7. Save the model. Click Save as own propellant… in the dialog. The program makes a new record " (fitted)" in your own database and keeps the photos of the powder. Select it in other loads with Select Propellant…. You can also click Apply to this load to put the fitted values into this load only.
  8. Fit again later with more loads: the fit uses all measurement series of the load, and the command-line tool csr_fitpowder (see Procedure 2) fits one model to several load files.

The fit is made for one load at a time. A powder that is fitted to one caliber and one bullet only can give wrong results in other cartridges. Check every new load with a measurement before you trust the model.