One of the first things wildcatters did with the .300 H&H case was to reduce the body slope and sharpen up the shoulder angle to increase powder capacity. A number of wildcats have been designed essentially this way, and after World War II commercial outfits started to follow suit.

Probably the first of these was Weatherby. Roy Weatherby followed the basic formula of blowing out the full length .300 H&H case. His new .300 used the double radius shoulder first seen on his .270 Magnum and retained a usefully long neck. Heavy bullets do not have to be seated deep into the case as they do with the short magnum cartridges, or even the standard length .300 Win. Mag. The flip side of this is that a long magnum length rifle action is required for the .300 Weatherby.

Roy Weatherby introduced his famous .300 Weatherby Magnum in 1948. He claimed a muzzle velocity (MV) of 3,300 fps with the 180 grain bullet, but the .300 Wby. Mag. actually tops out at about 3,200 fps from a 26 inch barrel. Current factory loads using a Hornady Interlock bullet claim a more realistic MV of 3,240 fps with 4195 ft. lbs of muzzle energy. This is achieved at the very high maximum average pressure of 65,000 psi.

The 2002 Weatherby catalog lists factory loads for several bullet weights, including 150 grain Hornady Interlock and Nosler Partition bullets at a claimed MV of 3540 fps. Weatherby offers 165 grain Hornady Interlock and Nosler Ballistic Tip bullets at a MV's of 3390 fps and 3350 fps respectively. The popular 180 grain weight is represented by Hornady Interlock, Nosler Ballistic Tip, Barnes X, and Nosler Partition bullets at MV's ranging from 3190-3250 fps. Heavy bullets are represented by the 200 grain Nosler Partition at a MV of 3060 fps and the 220 grain Hornady RN Interlock at a MV of 2845 fps. Unlike the lesser .300 Magnums, the .300 Wby. is a true ultra-long range caliber when used with bullets of 150-165 grains.

As with all .300 Magnum cartridges, factory loads with 180 grain bullets are the best sellers. Weatherby trajectory tables show the following for the popular 180 grain Hornady spire point bullet at a MV of 3240 fps: +3.1" at 100 yards, + 2.8" at 200 yards, 0 at 300 yards, and -9.0" at 400 yards. At 300 yards this bullet is still carrying 2635 ft. lbs. of kinetic energy.

The Barnes Reloading Manual No. 1 shows that with their 180 grain bullets the .300 Weatherby can achieve a MV of 2883 fps in front of 76.0 grains of RL22 powder, and a MV of 3172 fps in front of 80.5 grains of RL22. These loads used Weatherby brass and Federal 215 primers, and were chronographed in a 26" barrel.

The biggest advantage the .300 Wby. has over the standard (.30-06) length magnums is its ability to handle long, heavy bullets more efficiently. The Barnes Reloading Manual No. 1 shows a maximum velocity of 2,692 with their 250 grain bullet in front of 68.0 grains of IMR 4831 powder. This is 118 fps faster than the top load shown for the same bullet in the standard length .300 Win. Mag.

Several prominent rifle makers offer rifles in .300 Wby. Mag. caliber. It remains the most popular of all the Weatherby Magnum calibers. The .300 Weatherby is used all over the world, and ammunition is available in major centers catering to hunters from Anchorage to Nairobi. It has become one of the staple big game cartridges, and most of the major ammo manufacturers load for the .300 Weatherby. The world is lousy with .300 Magnum cartridges, most of which are redundant. The .300 Weatherby was one of the first and it is still the best of the breed.