A 300 Weatherby necked down to a 7mm. Rifles chambered for this round have standard throat with no free bore. In the early 1960's Mr Howard Wolfe a custom gunsmith and target shooter of Mifflinburg,PA. started playing with this cartridge for 1000 yard target shooting. It was reportedly first tested by RobertHutton of the Guns & Ammo Magazine Technical Staff in 1961 and 1962.

In October,1970 Mary Louise Devito of Willaimsport, PA used this cartridge with the Sierra 168 gr Matchking bullet in a heavy benchresr rifle to break the 1000 yard benchrest record. Her record group was 7 11/16 inches. Her rifle built by Howard Wolfe, was on a FN400 benchrest action with a 30 inch Hart stainless steel barrel 1 1/4 inches in diameter with a 1 in 9 inch twist. Her ammunition, loaded by her husband was as follows;
300 Weatherby case necked down to 7mm
primer 215 Federal
powder 87 grs. of H570
bullet Sierra 7mm 168 gr. Matchking
velocity 3254 feet per second
loaded overall length of round 3.725 inches 

This text is based on information from “Cartridges of the World”, Hodgdon reloading manual, the cartridge designer and/or own resources.