Odd you should bring the article up as I have the very same vintage Dupont IMR Guide pictured however mine is dog eared and worn. The references to the .375 H&H are close to my experiences with it for practice.
A friend was going to Alaska and was lamenting the fact his .35 Whelen rounds were costing him a fortune. I offered to assemble some 158gr .357 (.358 dia) cast for his practice sessions of offhand, sitting, kneeling, and off sides of trees and such to prepare him for his hunt with a Ruger 77. Cutting costs only more by making the practice loads from the mountain of LC 30.06 brass I have. He was delighted, and though did not connect with a moose was glad to properly prepared. Now others with a .35 Whelen are coming out of the wood work seeking advice on 'practice rounds'. They are good to 100 yds and with a .3 cent primer, .12 cents of powder, and nearly free bullet, under .20 cents for a practice round is a bargain.

In my Whitworth .375 H&H the light jacketed perform well. So far I have not found a cast that is super accurate but good for snap shooting practice at 50-75 yds. I suspect I may be driving them too fast. More testing is needed.