What the Army researched and discovered from WWI to the late '50s was that the average human -a draftee, and that includes women - can't handle .30 Ball, either '06 or .308. The recoil is more than they want to handle, over the threshold, and it significantly affects accuracy.
Sure, trained shooters with extensive practice can handle .300WSM or whatever the latest cool sniper caliber is. They ain't average. Those guys don't shoot a combat load of it every day, either.
A combat load is about 300 rounds, and sometimes you shoot double or triple that if things get intense. Hopefully. You have to be alive to do it.
That's why the Army dropped down to the .223 - it increase accuracy. The ballistics also matched the effective range of power needed for the reality of the battlefield. Soldiers weren't capable of hitting much beyond 150 yards, and they couldn't control more than 500 yards of territory with small arms fire. It takes crew served heavy weapons, artillery, and aircraft beyond that.
Therefore, the effective recoil limit for the average human is in the .223 to .30-30 range, which includes another round, 7.62 x 39, the universally regarded AK caliber. It should be very apparent there is a common threshold - 8 to 10 pounds.
Check it yourself, you can see it here:
http://www.chuckhawks.com/recoil_table.htm
Here's another comparison, the National Service Rifle allows either 5.56 or 7.62, the top contenders shoot the M16 in 5.56. One reason is it's inherent accuracy, which is less expensive to attain, another is the rapid fire course - less recoil means you get on target quicker, and the scores are always higher in that regard, which gives the M16 the edge over the M14/M1.
Same for three gun, in the early years, the .223 was outlawed, including .30 wildcats similar to the Blackout. Once the shooters brought pressure to bear allowing it, few choose anything bigger than 7.62x39. Same for carbine courses - they don't disallow .308 for them, shoot 1,000 rounds over a two day weekend and get back with us on that.
Strip all the masculine posturing and oneupmanship out of the caliber wars, and you find when the smoke (and mirrors) clear, there is a limit to how much people want to be kicked. It's really not that much. I will take every opportunity to shoot larger, of course, and did all I could when it was free. 100 rounds of .50BMG is a lot of fun, every round of it was behind an M2 on a tripod - not shoulder mounted. Even the Army doesn't do that.
And now back to the fantasy of superheros blasting away with magnums with no ill effects whatsoever. Arnold S. has no lack of competition on the internet.
