Hell I would love to be 50 again.
when I was 50, I could still see to shoot well, didn't have as much brick dust in my eyes...
I don't take personal offense at "dude", though I might remind our younger "dudes" that it didn't always mean "bro, buddy, pal..etc. Once upon a time, still in living memory for some of us, "Dude" meant you didn't know what you were doing. Think "dude ranch" for city slickers, who didn't know how to ride, etc...
I'm a curmudgeon, not denying it. And I do get a bit peckish about terminology. What I'm seeing with the requirements for a "practical rifle for civilians" seems more to be a practical rifle for military use, instead.
Since I haven't read the book you mention, it wouldn't be just talking to a wall, it would be talking to a blank wall.
I am, however familiar with a lot of what Cooper wrote discussing his Scout rifle concept. Some of the features he thought useful have been derided by critics, mostly because the military doesn't operate in a way where they would be useful, TODAY.
Cooper built at least one of his prototype Scout rifles using a Remington 600 action. I have several 600s, and while not perfect they are very good and close to Coopers concept in several important aspects.
Do like the SMLE!
And certainly in the 'practical bolt gun' category, it's a great choice if you can readily source .303 Brit ammo or the components.
Despite the "antiquated" rimmed case it uses, the SMLE is, arguably, the best combat bolt action ever fielded. Hell on case life, though.
If you are talking civilians, not tied into any resupply net, then all the ammo you have is all the ammo you have. You are the supply net, and so, any caliber and cartridge you stock pile is just as "practical".
Choosing something you might be able to get from someone else would make resupply simpler, or give you more options, but how likely is that to be something needed, IF it does actually occur?
I guess the biggest problem I have with calling this or that "practical" is that it implies that anything not in that group is impractical. Reality is that what is practical or impractical can vary hugely with the situation.
Most folks hunting elephant wouldn't consider a 5.56mm AR to be practical for that use. Most people don't shoot prairie dogs with a .458 Win mag, either. (though it is a fun challenge with the right handloads!
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Make a game (call it training if you like) with what ever rules you like. Be clear about the rules, and call it anything you like, its yours. But don't confuse game practical with real world practical, because while there is overlap, there are also distinct differences, at least as I see it.