6.5 Wssm, Hmm, Didn't Rem have something like that back in '65
No, but they did have one similar to a 6.5 WSM in the 1960s - the 6.5 Remington Magnum. Same idea as today, put a short cartridge in a short, light action - but it didn't sell back then. The same rifle in .350 Rem Mag almost became a collectors item as it fit the bill for a short light DG rifle. The 6.5 RM has less capacity than a 6.5 WSM would, but real-world performance would be very similar.
The .404 Jeffery-based cartridges won't work in standard AR-15 sized rifles, there isn't room for all that diameter with safety and the pressures are likely too high. In an AR-10 package, perhaps.
Colonel Cooper was convinced that the world had more than enough cartridges and with only my 53 years on this earth to go by I believe he was right....
Sure, and many gunwriters of the late 19th century believed that the newfangled "white powder" was a flash in the pan and offered nothing new they needed in rifle performance.
What many forget is that without "new and improved" cartridges, rifle makers would sell fewer rifles - this is the fact of modern marketing and those who fail to grasp the concept are doomed to lose. With fewer rifles sold, there would be fewer rifle makers and the rifles would cost more. Simple economics, whether we like it or not. So the bottom line is that the WSM/WSSM/RSAUMs are good for
all of us, we just don't have to buy them if we don't want to do so. That's what my 55 years on the planet have taught me anyway.
.