Free recoil is momentum math, and momentum math is exact: bullet momentum plus powder-gas momentum, divided by rifle weight, gives rifle velocity; rifle weight and velocity give energy. The gas term uses the SAAMI convention of 4,700 fps for the powder gases.
The charge field is arithmetic input only — take any charge weight from your own current published manual for your own load work. TruingLog publishes no charge data.
Read this before you rely on any number here. Predictions use the standard G1/G7 drag models and the data you enter — they are estimates, not measurements, and they are never load advice. Confirm with live fire at distance. For anything you load yourself, work only from current published manuals (Hodgdon, Sierra, Hornady, Lyman), start low, and work up. TruingLog publishes no load recipes and suggests no charge weights.