A couple of pressure questions

[Classicvette63]

Why are some powders max loading well under peak pressure? Example, in Hogdons manual, the max load for a 158gr hp in a 357 magnum with either H4227 or H110 generates over 40,000 c.u.p. Lilgun is kept at a max for that load of 25,800c.u.p. Why is that? If the gun can take 40,000cup of H110, why can't it take 40,000cup of Lilgun?

Another question I have is, I see how the pressures of new cartridges are way above older, albeit modern rounds. How far can they go in pressure? If you had the steel or alloy to hold 100,000 or more, would it be worth it? Is there some point of diminishing returns?