Nickudu posted an artice co-written by Elmer Keith "I'm for Big Bores and Heavy Bullets".

Stating, "In conclusion:
No less than .33 cal...
Not less than 250 grain bullet...
and velocities up to but not over 2,700 fps...

What gun was he using to come up with this conclusion? Any other cartridges fit this with a non belted case in a standard action?

Elmer was using his wildcats .333OKH and .334 OKH ( ONiel,Keith,Hopkins) the .333 was a necked up 30-06 and used .333 Jeffery bullets, and the .334 wused the .300 H&H necked up or the .375 H&H case necked down. Barnes also built bullets for them to use. Ultimatly the wildcat loads would develop into the .338 Winchester and the .340 Wheatherby.

Could have been talking about the 35 Whelen.
He was known to be fond of that cartridge.
"just a Guess as it meets most of the Criteria"

The 9.3x62 would fit the criteria as well as the 375 Scovill.