The 7mm-300 Weatherby Magnum

By Chuck Hawks

This is an old wildcat whose time has come. Not that everyone needs a seven based on such a huge case (does anyone?), but the consumer demand is there. Witness the interest in and commercial success of other big case 7mm Magnums, such as the 7mm STW and 7mm Remington Ultra Mag., not to mention all of the proprietary super sevens.

It would seem to me to be a natural for Weatherby to introduce a big seven based on their popular .300 Magnum case. Wildcatters have been turning out this cartridge since soon after the commercial introduction of the .300 Weatherby Magnum parent case in 1948, so it is hardly a new concept. It predates the 7mm STW and 7mm Ultra Mag by decades!

The .300 Weatherby Magnum case was originally created by fire forming (blowing out) a full length .300 H&H Magnum case for maximum powder capacity. The .300 Weatherby is a SAAMI standardized cartridge, and commercial .300 Weatherby brass is easily available.

The 7mm-300 Weatherby wildcat is created by simply necking-down the .300 Weatherby case to accept standard 7mm (.284") diameter bullets. Load the resultant case to the same 54,000cup/65,000 psi MAP that applies to the .300 Wby. Mag. and the result is truly a maximum performance 7mm cartridge. The 7mm-300 Wby. is just about the ultimate ultra-long range combination CXP2/CXP3 big game cartridge.

The 7mm-300 Weatherby is very similar to the established 7mm STW, already a SAAMI standardized cartridge, which is probably what has kept Weatherby from introducing their version of a full magnum length 7mm cartridge. The 7mm STW is also loaded to a MAP of 65,000 psi, so there is really no performance difference between the two. But I suspect that Weatherby marketing, the availability of Weatherby rifles, and the cachet of the Weatherby name would make the 7mm-300 Weatherby a commercial success--surpassing the 7mm STW and 7mm Ultra Mag in sales--if it were it were introduced commercially.

The 7mm-300 Wby. can drive a 140 grain bullet to a muzzle velocity of about 3500 fps or a 160 grain bullet to a MV of about 3200 fps within permissible pressure limits using canister powders available to reloaders. The Weatherby/Norma loading trust, using non-canister powders and moly-coated bullets, might achieve velocities 100 fps higher in factory SAAMI or CIP standardized factory loads. This would allow the 7mm-300 Wby. to out perform the 7mm Ultra-Mag as factory loaded by Remington, and make the 7mm-300 the velocity champion among commercial 7mm cartridges.

That is hypothetical, of course. But what is certain is that the 7mm-300 Weatherby, as it stands right now, is one heck of a high performance wildcat!

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Copyright 2005, 2014 by Chuck Hawks. All rights reserved.