Thank you for your questions...if I wrote regressive I apologize, it should have been written degressive. I mentioned degressive and neutral powders as it related to the .38 Super N105 loading, N105 being a neutral powder = a higher pressure/travel curve with a lower peak chamber pressure vs a degressive powder that has a higher peak pressure, but this type of powder has a rapid pressure drop and low pressure/travel curve.
I don't know if powders from other companies use this terminology or not, maybe it's a VV thing, regardless, 3N38 and N105 are top performers in certain combinations.
The VihtaVuori 4th edition (ISBN 978-951-97156-3-6 should anyone wish to do an interlibrary loan) has 11 pages devoted to the "Behaviour of Nitrocellulose Powders". If there are degressive powders (handguns), it's implied that there are progressive powders (rifle) and neutral powders (3N38 and N105) fall in between.
Powder types like ball (spherical), flake and non-perforated grain designs are considered to be degressive powders. Perforations increase the burn surface, single perforated grains are considered to be neutral, while 7-perforated and 15-perforated grains are considered as progressive powders.
The burning rate of powder composed of kernels without any perforations or surface treatment is related to the surface area of the grain available for burning at any given pressure level. The change in the surface area that is burning combustion is described by a so-called form function. If this area increases the form function does likewise and its behaviour is termed "progressive". If the form function decreases, in other words the total powder surface area that is burning decreases as the combustion progresses, its behaviour is said to be degressive. If the flame area remains constant throughout the combustion process, we describe it as "neutral" behaviour.
As you wrote, powder grain size can be small, medium and large...with three different pressure curves.
Put another way, using VV max loading pressure of 33,350psi, 38 Super (VV same operating pressure 10mm), a 125gr bullet with a neutral powder, N105 can attain ~1500fps, a degressive powder (any VV powder faster than 3N38) would be well over that pressure threshold to reach 1500fps.
The work which the combustion gases perform while accelerating the bullet can be expressed through the pressure/travel curve as...
work = cross-sectional area of barrel * pressure/travel curve area
The appropriate formulae were printed, but I am unable to write some of the symbols used for these mathematical calculations.
With modern powder designs, pressure under the curve area needs to be included in bullet acceleration and exterior velocities.
I prefer the way VihtaVuori displays their powder burn rates, in columns compared to using numerical lists. Burn rate charts are approximate, with that in mind, VV charts N105 closer to AA #7 than AA #9. I have not used N105 to load in 10mm, but it performs very well in my handloads for .38 Super/125gr and .44mag/200gr.
I no longer load JHPs max for 10mm because of lack of bullet integrity beginning ~1300fps, now my velocity goal is ~1250fps...it does make for faster split times and consistent penetration depths.