I know on a lot of old lever rifles, groove diameters can vary greatly. The .44/40 - seems the range is about from .426 to .436. If one is considering an 8mm bullet in a .32/40, knowing the groove diameter would be a helpful thing. For all you know, an 8mm bullet might be a better choice for that bore than the standard .321 bullet. I believe it is my older Lyman loading manual that specifies the individual firearm they used for load development along with the measured groove diameter of that particular firearm. For example, I seem to recall they used a Remington M14 for the .32 Remington and the groove diameter of that particular rifle was .319. So, if that were my rifle, knowing that would certainly help me decide that I probably didn't want to use an 8mm jacketed bullet.
