So your saying as long as the powder is burning it's not makeing pressure and heat? Larry
Powder burn is a chemical reaction. It starts with the primer, then it accelerates and burns more rapidly, then it reaches a "peak" then it starts to fizzle out and wind down. Easy to visualize, just imagine the last time you played with fireworks.
The Z1 line is the "peak" of the burn. Everything past that is the "fizzle", so to speak.
Pressure happens based on two things. One is the burn of the powder making pressure/gas, the other is the
when (or time component) of that pressure and gas. The reason the
when matters is that as soon as the pressure starts building the bullet starts moving. When the bullet moves the available space for the expanding gas is enlarged. Since the burn is accelerating and the bullet is also moving enlarging the space, you've got a moving target for where/when Pmax is going to occur. The longer it takes to hit Pmax the bigger the space available to do so, and as a result the more powder you can use and the more energy involved. This is precisely the reason why for a given max pressure, slower burning powders make higher velocities.
Once you are past Pmax the bullet is accelerating ever faster, the volume rapidly expands, and pressure drops as a result of the expanded volume. Simultaneously the powder, once past the Z1 line is in the "fizzle" stage and is mostly burned up already.
While Quickload doesn't draw you a line showing the percentage of powder burn, you can back into that figure by just changing the barrel length and seeing what the percentage of powder burn is. What you'll find is that 65-75% of the powder is burned in the first 4 inches, by 10 inches it's 90-95% burned, and all this burn is taking place a "digressive" manner meaning it's less energetic than the initial portion of the burn.
So essentially between 10 inches and 17 inches in the barrel, you have about 5% of the powder finishing up its "fizzle" in the lowest pressure part of the firing cycle when the pressure is falling rapidly.
All this is a bit long winded, but hopefully it helps you understand that what you've been saying isn't technically correct. Note that I don't disagree with you that H4350 is probably easier on the throat than Varget... I think that makes sense. Just not the way you've been saying it.