Daryl,
Please re-read what I actually said.
NOWHERE have I stated that "there were no high pressure rounds chambered in DR's".
What I did say was..........

>>>>> When talking about large bore big game cartridges of .400 cal and larger, 55,000psi to 63,000psi are bolt gun or single shot pressures, not double rifle pressures.....

Once you get into the large bore double rifle NE cartridges, pressures of 55,000psi to 63,000psi are unheard of. They just don't exist, and for good reason.
With large bore Flanged NE cartridges, here is an idea what you are dealing with. <<<<<

Please note that I was specifically talking about "large bore double rifle NE cartridges", which are, "large bore flanged NE cartridges".
The .458 Win mag and the 375 H&H belted magnum do NOT fall into that category. They are not flanged, and they were not designed specifically for double rifles.
Also the 375 mag does not fall into the "cartridges of .400 cal and larger" which I clearly mentioned in my post.

Why on earth would I ever suggest that " there were no high pressure rounds chambered in DR's", when one of my own most hunted with doubles is chambered for the 7x65R, which is a (CIP) 55,000psi cartridge?
That particular DR was also available in 270 Win, a cartridge rated at (CIP) 62,000psi!

The .375 and .458 belted magnums have certainly been chambered in DR's, but they are not, and never will be, "large bore Flanged NE cartridges".

My involvment with DR's goes back quite a while, about 30 years, and to suggest that I "oops forgot" that the 375 and 458 magnums have been chambered in DR's is pretty funny.