Brass Fetcher Ballistic Testing

The 257 Weatherby Magnum cartridge is a great cartridge choice for long-range hunting of small and medium game animals. With a kinetic energy at the muzzle of 2900 ft-lbf, this firmly places the cartridge in the top end of the medium-power rifles such as 308 Winchester. The wildcard in this comes with the fact that the bullet weight for the weapon is limited by the diameter of the bullet and the twist rate of the barrels that are commonly available. Most common bullet weights for this caliber range from 90gr to 120gr and usually feature bullets with massive expansion and thin jackets. This is great for hunting predator animals (small predator animals) at long ranges where there isn’t a need for excessively deep penetration and there is still a desire for bullet expansion despite the loss of bullet velocity encountered by traveling a long distance through the air.

Owning a 257 Weatherby firearm is a rewarding experience because the cartridge ’seems’ like its going to kick a lot but it does not. The reason for this is that the cartridge burns a lot of propellant but propels a lightweight bullet to high velocity. This gives magnum-like performance with a truly ’magnum’ muzzle flash and blast. There is a concern with rifles that use a lot of propellant and have a small bore diameter relative to the chamber diameter and that concern is throat erosion. The throat area of the rifle barrel is the unrifled portion of the barrel immediately in front of the cartridge neck and before the rifling. Magnum rifles utilize high chamber diameter to bore diameter ratios and longer barrels to burn more propellant to add to the bullets acceleration as it moves down bore. This leaves more solid propellant grains moving down bore and this effectively sands or ’erodes’ the first part of the rifling—reducing the pressure behind the bullet which reduces the bullets velocity and causes ’in-bore balloting’ which is the sideways/upwards movement of the bullet inside of the bore. Throat erosion will reduce downrange lethality and accuracy.

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10-percent Ballistic Gelatin Shots
See how well this caliber stacks up against the FBI performance requirement of expansion and 12.0” or deeper penetration depth.


20-percent Ballistic Gelatin Shots
See how well this caliber stacks up in military-standard performance evaluations.

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