I have been told, and I suspect that it is very accurate information, that the .300 Weatherby Magnum is the most popular cartridge in the Weatherby line of high intensity cartridges.
Roy Weatherby initially developed four cartridges in the mid-to-late 1940s. These were the .220 Rocket, based on the .220 Swift case, and the first three of the Weatherby line of magnums, the .257 WM, .270 WM, and .300 WM. Weatherby's brainchild developed a muzzle velocity of over 3500 fps with the 150 grain bullet, almost 3400 fps with the 165 grain, 3250 fps with the 180 grain, and over 3,050 fps with the 200 grain bullet. For the time, those velocities were eye-openers, and even today are still sizzling down range.
The ballistics provided by the .300 Wby. made it about as close to ideal as one is apt to find for the all-around one-gun hunter. One example is that of C.J. McElroy, the founder of Safari Club International. Mr. McElroy hunted all over the world and for many years used nothing but a Weatherby Mark V rifle chambered for the .300 Wby cartridge. He used it for almost everything he hunted. I knew Mac quite well and last time I saw the rifle, it was about as dilapidated as a rifle could be and still function.
Mac was not a gun nut and to him, the rifle was nothing but a tool. He once told me that the rifle was like an extension of his arm in the field. Finally as the effects of his advanced age finally began to affect him, he switched rifles for the remainder of his hunting years. It was another Weatherby Mark V rifle, but chambered for the 7mm Wby. instead of another .300.
Another well known international hunter that used nothing but a .300 Wby. chambered Mark V for his hunting was Elgin Gates. Gates wrote numerous magazine articles about his exploits with the rifle, and also wrote a book or two about his adventures with it. Both McElroy and Gates could have afforded most any rifle they wanted, but both were more than pleased with their Weatherby rifles.
Well known custom rifle maker David Miller also is a one-rifle hunter. His hunting rifle is one of his own make, but chambered for the .300 Wby. David specializes in chasing big Coues deer around the mountains of southern Arizona and northern Mexico. He has taken more trophy bucks than anyone I know or have ever heard of.
Now I fully understand that a very large Coues buck is not a very large animal, and a rifle as powerful as the .300 Wby. is not needed to slay such a buck. However, big trophy bucks are very wary animals, and if spotted at all, are generally seen at long ranges. Miller and his .300 have taken several book sized bucks at ranges exceeding 500 yards, a few exceedingly so.
Personally, I have owned but one rifle chambered for that cartridge, a German-made Mark V that I bought in Germany at a US Army Rod & Gun Club in Stuttgart about 1964. I kept it for a while, but at the time had no real need for it, so traded it for something else, I've long since forgotten what. It was a pleasant rifle to shoot, very accurate with factory ammo (I hadn't started handloading at the time), and an attractive rifle, even with its California styling. At the time, the styling was acceptable to me, although these days, it gives me the “vapors” as O'Connor used to write.
The Weatherby line of “hyper” velocity cartridges was the earliest of the genre that I'm aware of. There were few, if any coming before, and plenty coming after. The downside, if it is a downside, is that in order to achieve such velocities, the cartridge is loaded to the max pressure wise, or very close to it. They also have considerable free-bore in the chamber to tame the high pressures somewhat.
Still, I've not heard of a Weatherby rifle so chambered causing any damage. I have heard of a few blown primers, but that was about it. For the one gun hunter, a much worse choice could be made than the .300 Weatherby.