I'll add a few points to Bob's excellent points:
There really weren't gun magazines as we know them until after World War II. American Rifleman was about it, and back then AR was more technical and devoted to match results than it is today.
As I recall, Outdoor Life had the largest circulation of any of the hunting/fishing/shooting camping magazines until Field & Stream overtook it a couple decades after WWII, and even then F&S didn't beat it by much. And OL was THE outdoor magazine selected to be sent to overseas troops during WWII, introducing O'Connor to millions of servicemen.
The largest-circulation magazine Elmer Keith ever worked for was American Rifleman, which was a smaller and less influential than either OL or F&S in those days. Keith eventually quit AR to work for Guns and then Guns & Ammo, both much smaller shooting magazines started after WWII. Eventually G&A's circulation became medium-large, but even at its peak it never matched the numbers of Sports Afield, the smallest of the so-called Big Three outdoor magazines.
O'Connor's influence on hunting firearms at the peak of the Big Three period, roughly the 1950's through the 1970's, could probably be compared to major sports columnists in big-city newspapers back then. Of course, those newspapers have also lost considerable circulation now, and many have even disappeared--along with real writing. Instead we're in the era of sound bites and controversy, whether on the Internet, radio or TV.
