.257 Weatherby Magnum

.257 Weatherby Magnum
Type	Rifle
Place of origin	USA
Production history
Designer	Roy Weatherby
Designed	1944
Manufacturer	Weatherby
Produced	1948-Present
Specifications
Parent case	.375 H&H Magnum
Bullet diameter	.257 in (6.5 mm)
Neck diameter	.285 in (7.2 mm)
Shoulder diameter	.492 in (12.5 mm)
Base diameter	.512 in (13.0 mm)
Rim diameter	.5315 in (13.50 mm)
Rim thickness	.051 in (1.3 mm)
Case length	2.545 in (64.6 mm)
Overall length	3.209 in (81.5 mm)
Rifling twist	1 in 10
Primer type	Large Rifle (magnum)
Ballistic performance
Bullet mass/type Velocity Energy 87 gr (6 g) SP 3,825 ft/s (1,166 m/s) 2,826 ft⋅lbf (3,832 J) 100 gr (6 g) SP 3,602 ft/s (1,098 m/s) 2,881 ft⋅lbf (3,906 J) 117 gr (8 g) BST 3,400 ft/s (1,000 m/s) 2,952 ft⋅lbf (4,002 J) 120 gr (8 g) Partition 3,305 ft/s (1,007 m/s) 2,910 ft⋅lbf (3,950 J)
Test barrel length: 26 Source(s): Weatherby

The .257 Weatherby Magnum is .25 Caliber (6.3 mm) belted bottlenecked cartridge. It is one of the original standard length magnums developed by shortening the .375 H&H Magnum case to a length of around 2.5 in (64 mm). Of the cartridges developed by Roy Weatherby, the .257 Weatherby Magnum was known to have been his favorite cartridge. The cartridge currently ranks third in Weatherby cartridge sales after the .30-378 Weatherby Magnum and the .300 Weatherby Magnum.

The .257 Weatherby Magnum is among one of the flattest shooting commercial cartridges. It is capable of firing a 115 gr (7.5 g) Nosler Ballistic Tip bullet at 3,400 ft/s (1,036 m/s) generating 2,952 ft⋅lbf (4,002 J) of energy which is comparable to factory loadings of the .30-06 Springfield and the .35 Whelen.

Discrepancies between the metric and U.S. diameters of the bullet may cause some confusion. A .257 bullet has a metric bullet diameter of 6.53 mm. However, in Europe cartridge designation nomenclature for a large part relies on the bore diameter. As the bore diameter of the rifle is .250 inches this would make the .257 Weatherby Magnum a 6.3 mm caliber cartridge rather than a 6.5mm caliber cartridge.

Cartridge History

The .257 Weatherby Magnum was designed in 1944 and introduced commercially in 1945 by Roy Weatherby as a wildcat cartridge. The original cartridge was developed using the H&H Super 30 (a close variant of the .300 H&H Magnum which in turn is based on the .375 H&H Magnum) shortened, blown out and necked down to accept a .25 caliber (6.3mm) bullet. Together with the .270 Weatherby Magnum, 7mm Weatherby Magnum and the .300 Weatherby Magnum, the .257 Weatherby Magnum were the earliest cartridges introduced by Roy Weatherby.

Beginning in 1948 Weatherby began offering loaded ammunition for the cartridge. The cartridges were formed using Winchester .300 H&H Magnum and later brass manufactured by Richard Speer before being loaded in house. Until then the cartridge was only available as a component brass which would require being loaded before use. However, due to space and organizational constraints Weatherby began looking for a source of ammunition for his cartridge. The search which began culminated in 1951 with Norma Projektilfabrik being awarded a contract to produce ammunition. Since then, all Weatherby Ammunition has been manufactured by Norma with the exception of a brief period of time between 1963 and 1964 when production moved to RWS/Dynamit-Nobel, a company which had entered into partnership with Weatherby.

Ever since the release of the .257 Weatherby Magnum it has remained one of the more popular cartridges in terms of Weatherby sales.

Design & Specifications

The .257 Weatherby Magnum shares the same cartridge case as the .270 Weatherby Magnum and the 7mm Weatherby Magnum. The .375 H&H Magnum served as the parent cartridge for the case design. The .257 Weatherby Magnum was one of the first cartridges which used the shortened, blown out and necked down .375 H&H Magnum case and served as the forerunner to the standard length magnum cartridges such as the 7mm Remington Magnum and the .338 Winchester Magnum. There has been some speculation that Roy Weatherby may have used the full length .375 H&H Magnum case if he had slow burning powders available today when the cartridge was designed. The shortening of the case allowed for the more efficient use of the slow powder of the day, IMR 4350; a powder which would not have provided any great advantage for such cartridges as the .257 Weatherby Magnum or the .270 Weatherby Magnum if such cartridges utilized the full length H&H case. Today, IMR 4350 is considered too fast a burning propellant for the cartridge which comes into its own with the slowest burning powders now available.

Both SAAMI and the CIP have published specification for the cartridge. The CIP standards for the cartridge were published in January 1994.

SAAMI recommends a barrel rifling contour of 6 grooves with a bore Ø of .2505 in (6.36 mm) and a groove Ø of .257 in (6.5 mm) with each groove being .098 in (2.5 mm) wide. The recommended optional twist rate is one revolution in 10 in (250 mm). Both SAAMI and Weatherby recommend a freebore of .378 in (9.6 mm).

The .257 Weatherby Magnum has a case capacity of 84 gr. of water (5.45 cm³). Sources such as Lyman and Weatherby's pressure rating suggest maximum average pressure limit of 66,000 psi (4,600 bar). CIP limits the .257 Weatherby Magnum to a maximum average pressure of 4,400 bar (64,000 psi).

Performance

The .257 Weatherby is known for its long range performance and is considered an accurate flat shooting cartridge. Initially due to the cartridge’s high velocity the cartridge exhibits less bullet drop than most other cartridges. However, due to lower ballistic coefficients of these bullets velocity and therefore energy is shed more quickly.

Weatherby’s B25780TTSX, B257100TSX and the N257115BST ammunition have point blank rages of 369 yd (337 m), 350 yd (320 m) and 323 yd (295 m) respectively. Thus no hold over is necessary when shooting at game at these ranges given the rifles is zeroed correctly to accomplish this task.

When sighted in for 300 yd (270 m) the bullet of Weatherby’s N257115BST ammunition has only dropped 21.9 in (56 cm) at 500 yd (460 m) and retains 1,347 ft⋅lbf (1,826 J) energy. Compared to the Winchester’s .270 WSM SXP270S ammunition show a bullet drop of 24.5 in (62 cm) but retains 1,552 ft⋅lbf (2,104 J). The N257115BST bullet retains enough energy to be effective on deer out to 550 yd (500 m) while the SXP270S's bullet extends this range out by a further 100 yd (91 m) although both the Weatherby’s and Winchester’s ammunition start with roughly the muzzle energy.

Weatherby guarantees a 1.5 MOA accuracy with their ammunition in a Weatherby rifle.

Sporting Usage

The .257 Weatherby is a hunting cartridge and has not been for a large part adopted into any other shooting discipline. A reason for this has been the poorer selection of bullets and the lower sectional density and ballistic coefficients of those bullets. Due to the cartridge’s use of lighter bullets of a quarter bore diameter the use of the cartridge should be restricted to medium game species. The cartridge comes into its own when and where shooting over long distances is required or anticipated. This is especially true in habitats major grasslands or mountain ranges.

The .257 Weatherby makes an ideal pronghorn cartridge. Due to the habitat of the species and its wariness, shooting distances are generally longer than other species in North America. The cartridge is well suited for smaller deer species such as whitetail and mule deer although it is used as an elk and caribou cartridge regularly in North America.

The cartridge has had success against mountain sheep and goat whether it be in the Alps, Rockies, Caucasus, Pamir or the Himalayas. Shooting distances a typically long and the .257 Weatherby is able to reach out to the long ranges required to take the game.

Should the cartridge be employed for plains game in Africa use should be restricted to game species under 440 lb (200 kg). The cartridge is effective against smaller plains game species such as gemsbok, waterbuck, nyala and impala.

The .257 Weatherby is used as a small predator. Smaller predators such as lynx, cougar, bobcat, fox, coyote, and wolverine are taken yearly with the cartridge. While the .257 Weatherby can be employed as a effective varmint the cost per cartridge and the muzzle blast precludes its use as a varmint cartridge in large numbers. Furthermore, due to barrel heating and wear are a consideration when employing the .257 Weatherby for such duties were one would shoot long strings of shots in a short period of time. Due to the cartridges high velocity and use of lightly constricted bullets, the use of the cartridge as a small game cartridge is not recommended as there are far better choices available which do not destroy the meat as the .257 Weatherby does. If solids or FMJ bullets are used this should not be an issue with regard to small game intended for the table.

Roy Weatherby took the .257 Weatherby Magnum to Africa and took an African Cape buffalo with a single shot to prove to himself that it could be done. Although the cartriage has been used against lion and bears the cartridge is ill suited for dangerous game species as it lacks bullets with good weights and sectional densities to be considered an even a moderately effective cartridge against such game.

Rifles & Ammunition

.257 Weatherby Magnum Ammunition

Ammunition	Bullet	Muzzle Velocity	Muzzle Energy	MPBR/Zero
Weatherby B25780TTSX	80 gr (5.2 g) Barnes TTSX	3,870 ft/s (1,180 m/s)	2,661 ft⋅lbf (3,608 J)	369 yd (337 m)/317 yd (290 m)
Weatherby H25787SP	87 gr (5.6 g) Hornady SP	3,825 ft/s (1,166 m/s)	2,826 ft⋅lbf (3,832 J)	356 yd (326 m)/209 yd (191 m)
Weatherby G257100SR	100 gr (6.5 g) Norma SP	3,500 ft/s (1,100 m/s)	2,721 ft⋅lbf (3,689 J)	318 yd (291 m)/274 yd (251 m)
Weatherby H257100SP	100 gr (6.5 g) Hornady SP	3,602 ft/s (1,098 m/s)	2,881 ft⋅lbf (3,906 J)	345 yd (315 m)/296 yd (271 m)
Weatherby B257100TSX	100 gr (6.5 g) Barnes TSX	3,570 ft/s (1,090 m/s)	2,731 ft⋅lbf (3,703 J)	350 yd (320 m)/301 yd (275 m)
Weatherby N257110ACB	110 gr (7.1 g) Nosler Accubond	3,460 ft/s (1,050 m/s)	3,925 ft⋅lbf (5,322 J)	334 yd (305 m)/284 yd (260 m)
Weatherby N257115BST	115 gr (7.5 g) Nosler BT	3,400 ft/s (1,000 m/s)	2,952 ft⋅lbf (4,002 J)	332 yd (304 m)/282 yd (258 m)
Weatherby H257117RN	117 gr (7.6 g) Hornady RN	3,402 ft/s (1,037 m/s)	3,007 ft⋅lbf (4,077 J)	308 yd (282 m)/266 yd (243 m)
Weatherby N257120PT	120 gr (7.8 g) Nosler Partition	3,305 ft/s (1,007 m/s)	2,910 ft⋅lbf (3,950 J)	318 yd (291 m)/270 yd (250 m)
Values courtesy of the Weatherby. MPBR/Zero values courtesy of Big Game Info.

Criticism

The .257 Weatherby Magnum is one of the most overbore cartridges available. The cartridge is more overbore than the .264 Winchester Magnum and the 7mm Shooting Times Westerner but less than the 7mm RUM and the .30-378 Weatherby Magnum. The consequence of burning a large quantity of powder and driving a bullet faster is poor barrel life and throat erosion all of which affects accuracy and usable life of the firearm. Giving the barrel time to cool between shots and following recommended cleaning procedures will help mitigate this issue and extend the usable life of the firearm chambered for this cartridge.

See also

• Weatherby
• .25-06 Remington
• .25 WSSM
• .257 Roberts
• List of rifle cartridges

References

• The .257 Weatherby Magnum by Chuck Hawks
• .257 Weatherby Magnum at The Reload Bench

External links

• In Praise of the .257 Weatherby Magnum article in Shooting Times
• Ultra-Long Range Rifles and Cartridges by Chuck Hawks