Entering a load¶

The left half of a load tab has three input tabs, the right half shows the results.

Cartridge & gun¶

Shows the caliber (Select Caliber… replaces it) and a table of properties: designation, overall length, case length, case volume, bore, effective area, maximum permitted pressure, barrel length, twist length, seating depth and more. Below the table the drawings show the cartridge, the chamber and (when available) the powder.

The Sebert factor (0 to 1) is kept as the file has it, 0 included, and all models use it as it is (the Physical model no longer replaces 0 by 0.5 in the propellant impulse and the recoil). A value outside 0 to 1 becomes 0.5 when the load is opened; the panel accepts only 0 to 1. The report shows the value the simulation used.

Primer and start pressure.¶

The Primer (a drop-down: small or large, pistol or rifle, standard or magnum, .50 BMG) starts with the usual primer of the caliber. The start pressure, the gas pressure at which the bullet starts to move, is 250 bar plus the Additional Start Pressure for the bullet, the crimp and the case, as in the original program; a new load takes it from the bullet record (its start pressure minus 250 bar). Only the physical model uses the primer: it adds the difference between the primer type's start pressure and 250 bar (fitted to Hodgdon's published loads: Large Rifle 250 bar, the others 230 to 450 bar). For pistol and revolver cartridges the physical model starts at no less than 0.3 times the maximum permitted pressure, so there the primer usually has no effect. Loads of earlier versions and of the original keep their start pressure exactly.

Replacing the caliber.¶

After you choose another caliber, the program can also set barrel length, seating depth and charge to the defaults of the new caliber (tick the corresponding option in the selection dialog). The primer becomes the usual primer of the new caliber; the additional start pressure stays.

Projectile¶

Mass, diameter, length and the other bullet data. Select Projectile… replaces the bullet; tick Show only bullets that fit the caliber to narrow the list. The Initial Gas Pressure is the pressure at which the bullet starts to move and engraves. It is the primer’s start pressure plus the Additional Start Pressure of the Cartridge & gun tab; editing it changes the additional one. The Bullet friction is an extra resistance in bar that acts all along the barrel; it is always applied. Negative values are possible and describe low-friction bullets (the original’s database has values down to \(-100\) bar). For 362 rifle bullets the project records carry start pressure and friction values fitted to published loads. A load keeps the values it was made with until you select the bullet again.

Propellant¶

Powder charge, explosion heat, burn rate and the form-function values. Select Propellant… replaces the powder.

With the Physical Model, project powders also have physical burn values. They are kept in the load file. If they are missing, an orange banner tells you so and offers Use the physical values….

A load keeps its own copy of the powder values. If a database record of that powder was corrected after the load was made, or you edited the values in the load, a second orange banner says Powder values differ from the database. The load is still calculated with its own values. Use the database values… replaces them with those of the closest record (the charge and all other settings stay; Undo takes it back). A powder can have several records, so the banner appears only if no record has exactly the values of the load. With the Physical Model only the project’s records are compared, because the original database is not updated; with the other models all records count.

Editing values¶

Click a value in a property table to edit it. Values with a unit have a drop-down menu for the unit; the choice applies to this field only. Reset per-field units in the settings returns every field to the chosen unit system. Some fields are coded values (for example the Shotshell flag) and offer a list of choices.

Measuring a load¶

A good Case Volume is the single most important input after the powder. Measure a fired case by filling it with water and weighing it. Also measure the real bullet length and cartridge overall length and enter the mean values.

Shotgun loads¶

Calibers with Shotshell set to yes use their own model terms. Enter such a load as follows:

Projectile: mass = shot + wad (about 2.5 g for a plastic wad), length = height of the shot column plus the wad, diameter = bore diameter;
seated completely inside the hull: cartridge overall length = hull length, seating depth = projectile length;
Initial Gas Pressure = crimp release, about 20 bar.

The load also has the choices Shotshell Hull, Shotshell Wad and Shotshell Primer, each with three groups of similar parts (low, medium and high pressure). They change the pressure by up to about \(\pm 20\,\%\). Shotgun results are less reliable than rifle and handgun results.