I have that old Speer book. Matter of fact I have two of them because the one that I bought new in 1973 was falling apart pretty bad and I found another one a few years ago at a gun show for $10 so I snapped it up.
If you noticed, they used Real Guns for their load development. Back in those days just about everyone one did. Sure, the usual warnings were there to approach max loads with caution but they still were safe loads. In their guns anyway.
That load of 23 grains of 2400 was my go-to load for over a decade in my 3 screw Super Blackhawk. I liked the Sierra 240 grain JHC over the Speer but I used other makes of 240 grain bullets too. Remington made a good one back then. And yes, that load was hot. I had to pound my extractor to get the brass out. And, I as much as I hate to admit it now, was much too hot for me to shoot without flinching terribly. Smacked my hand like a Nolan Ryan fastball using no mitt. But goodness I loved shooting it. Cinder blocks, 1/4" mild steel, bricks, snakes, toads, elephants (pictures!) small trees, etc etc all fell to my mighty .44 Magnum.
But today loads are much more mundane than they were back then. SAAMI had a lot to do with that. Lawyers too. But if any of you have a hankering to try some of those older loads you most likely will be just fine doing so. But be warned, some of them are not very much fun to shoot and must might be the reason why 40 odd years later I still flinch when I shoot a handgun. Good a reason as any I suppose.