Most of what you allude to is true. I just think the platform sends bullets downrange at max pressures and compressed loads. When I was first reloading my first 375 years ago, I could never come close to the max loads listed in the manual I used. One powder that comes to mind is 4350, whatever was listed was way too much to squeeze in the case without compressing the hell out of it. I stopped trying getting max loads out of my 375 H&H's and if I wanted extra velocity without the over compression, I have my 375 Ultra conversion. It gave me a little more boiler room to play with.