There is a lot more than "the barrel" that ads to things.
First thing is first, what is "pressure"?
IF, and this is a BIG ASSumption, IF a company ONLY built brass by the metals handbook formula. Cartridge brass has a tensile strength of about 70,000psi, so when you notice expansion, guess where your pressures are?!
So what formula DID they use to make the brass? They aren't saying. That is a piece of what people see for " pressures".
Next is the primer. Again there is no "spec" for primers. So how "tough" they are can vary wildly. There is part #2.
Now the chamber, the bore. How much your brass has to stretch to conform; and how far your dies push things back also contributes. If you over work your brass, you will begin the work-hardening process. This will further skew things.
Now powder. Marketers like Hodgdon try and sell things like "extreme" miracle powders. MOST people won't even read Hodgy's info about it. If they did, they would see that there is very little info speaking to the science of it. Furthermore MANY of their examples aren't statistically valid differences.
The theory does work, but only in a very specific setting. As an example. Varget is, relatively speaking, temp insensitive in the 308, when using 150gr bullets. But it's a streaming pile of crap when used in the 223. Doesn't mean it won't group in the 223, just means if you think things are "extreme" in that setting, you are out to lunch.
Finally you have chamber time. The biggest challenge for any powder to be "insensitive" is brought on by a hot chamber. Letting cartridges sit in a hot chamber is bad juju.
More on the point of powder: remember that we, the canister-grade using reloader, is a waste market.
WC 846 is a non-canister powder. The original patented recipe is from about the 1930's, IIRC. It allows for a max amount of CaCO of 1%, anything under that is kosher. When Olin began segregating and anything that had less than 0.25% was produced, they called it WC844. Ask a random reloader if BL-c(2) and H355 is the same powder, they will look at you like you are on the short bus. When the truth is, they are the same. Ask them how long this miracle copper cleaner in CFE223 has been around, they'll tell you about 2012. The Tin/Bismuth compounds that clean copper were discovered by the French about 1900. WC842( which is where CFE223 comes from) has been produced by General Dynamics for over a Decade. Those compounds have also been in Win748 & Win760/H414 for MANY decades.
How many people use a volume device, for bloody weight?! Extruded powder has its burning rate controlled by geometry. Weight and volume are NOT the same damn thing. Extruded powders have a very tight relationship between Bulk Density and Burning Rate. IF you want consistent pressures with extruded, STOP weighing powder and throw a volume. Cutting grains will not affect anything. A consistent VOLUME will limit burning rate fluctuation MUCH more than a weight of powder.... Unless you think your powder "company" who won't give you nominal burning rate variance and Bulk densities can ONLY build A thing....
Ball powder has burning rates controlled by Coatings, with no tie to BD, or amount of Nitro Glycerin. Not as awesome to load that by volume, again, unless you don't load by volume; you use a volume device to get a weight....
Seek out work done by Dr. Denton Bramwell. Has done a bunch of good work on this, and the "extreme" properties of powder.
If you want to know what pressures are really doing, buy a testing system. The Pressure Trace strain gauge system is only about $4-500. Know for yourself.