.378 Weatherby Magnum

{{Short description|Rifle cartridge}}

{{Infobox firearm cartridge

| name = .378 Weatherby Magnum

| image = Munit01.jpg | image_size = 300px

| caption = .378 Weatherby Magnum, center

| origin = South Gate, California

| type = Rifle

| service =

| used_by =

| wars =

| designer = Roy Weatherby

| design_date = 1953

| manufacturer = Weatherby

| production_date = 1953-Present

| number =

| variants =

| is_SI_specs =

| parent =

| case_type = Belted, bottleneck

| bullet = .375

| neck = .399

| shoulder = .560

| base = .582

| rim_dia = .579

| rim_thick = .063

| case_length = 2.913

| length = 3.65

| rifling = 1 in {{convert|12|in|mm|abbr=on}}

| primer = Large rifle magnum

| is_SI_ballistics =

| bw1 = 300

| btype1 = Full Metal Jacket

| vel1 = 2925

| en1 = 5699

| bw2 = 300

| btype2 = Round nose

| vel2 = 2925

| en2 = 5699

| bw3 = 270

| btype3 = Truncated solid

| vel3 = 3060

| en3 = 5613

| bw4 = 270

| btype4 = Pointed soft point

| vel4 = 3180

| en4 = 6062

| bw5 = 260

| btype5 = Partition Type

| vel5 = 3140

| en5 = 5743

| test_barrel_length = 26 in (66 cm)

| balsrc = Weatherby {{Cite web |url=http://www.weatherby.com/products/ammo.asp?prd_id=11%2F |title=Weatherby |access-date=2018-11-26 |archive-url=https://web.archive.org/web/20070927085809/http://www.weatherby.com/products/ammo.asp?prd_id=11%2F |archive-date=2007-09-27 |url-status=dead }} / Nosler {{Cite web |url=http://www.nosler.com/index.php?p=11&b=3%2F&s=102%2F |title=Nosler |access-date=2018-11-26 |archive-url=https://web.archive.org/web/20070928132552/http://www.nosler.com/index.php?p=11&b=3%2F&s=102%2F |archive-date=2007-09-28 |url-status=dead }}

}}

The .378 Weatherby Magnum was designed by Roy Weatherby in 1953.FAQ at weatherby.com.{{Cite web |last=Jones |first=Allan |date=2021-04-05 |title=The .378 Weatherby Magnum |url=https://www.shootingtimes.com/editorial/378-weatherby-magnum/390467 |access-date=2024-08-27 |website=Shooting Times |language=en}} Although inspired by the .416 Rigby, it is an original belted magnum design with no parent case.Any Shot You Want, The A-Square Handloading Manual, pp. 479,480 The cartridge features a high powder capacity relative to its bore size, and can hold upwards of 7.13 g (120 gr) of powder. This consideration prompted the Federal Cartridge Company to introduce the 215 Magnum primer specifically for this round. The .378 shares the double radius shoulder design found on the other Weatherby magnum cartridges.

The impetus for the development of the .378 arose from Roy Weatherby’s extensive field testing conducted in African hunting grounds. Based on his safari experiences, he believed it to be desirable to improve the performance afforded by his preexisting .375 Weatherby Magnum by devising a larger cartridge more in keeping with the design philosophy of his small-bore cartridges, such as his .300 and .257 Magnums.Sierra Bullets Reloading Manual, Rifle, Second Edition, pg.287{{Cite web |date= |title=weatherby |url=http://www.nrainsights.net/first%20freedom/weatherby.asp |archive-url=https://web.archive.org/web/20070928033818/http://www.nrainsights.net/first%20freedom/weatherby.asp |archive-date=2007-09-28 |access-date= |website=www.nrainsights.net}}

To promote the .378, Roy Weatherby killed an African elephant with one shot at extended range. In order to gain access to markets across the African continent by accommodating the 10.16 mm (.40 caliber) minimum bullet size required for use on dangerous game in some countries, Weatherby soon necked the .378 to 11.63 mm (.458 caliber) and introduced the resultant cartridge as the .460 Weatherby Magnum in 1957.{{Cite web|url=http://www.weatherby.com/products/ammo.asp?prd_id=13|access-date=2020-01-14|archive-url=https://web.archive.org/web/20080808090925/http://www.weatherby.com/products/ammo.asp?prd_id=13|title=:: Weatherby : .460 Weatherby Magnum ::|archive-date=2008-08-08|url-status=dead}}

Considered a safari-grade cartridge, the .378 Weatherby Magnum is appropriate for taking all African game animals, including the African antelopes, Nile crocodile, hippopotamus, and the Big Five. Some hunters on the North American continent employ the .378 for American elk, brown bear, and polar bear. With proper bullet selection, the .378 provides a similar trajectory to and greater downrange energy than the .300 Winchester Magnum, .300 Weatherby Magnum, and .338 Lapua Magnum.

The .378 Weatherby generates considerable free recoil with full-power loads, for an average of 72 ft·lbf from a 9 lb rifle. This compares to 23 ft·lbf from a rifle chambered for .30-06 Springfield or 44 ft·lbf for the .375 H&H Magnum. However, the .458 Winchester Magnum generates 78 ft·lbf and the .458 Lott produces 86 ft·lbf of free recoil.{{Cite book |title=Hornady Handbook of Cartridge Reloading |date=2016 |publisher=Hornady Manufacturing Company |edition=Tenth |location=Grand Island, Nebraska}} It should also be noted that Weatherby Mark V rifles chambered in this cartridge are equipped from the factory with removable muzzle brakes that greatly reduce felt recoil.

The .378 has been responsible for numerous wildcat cartridges. It has been necked-down as the .22 Eargesplitten Loudenboomer and necked-up as the .475 A&M and .500 A-Square, and shortened to produce the .30-378 Arch (7.62mm), .338-378 KT, and .460 Short A-Square (11.63mm).{{cite book

| last = Ackley

| first = P.O.

| title = Handbook for Shooters & Reloaders

| edition = 12th Printing

| series = vol I

| orig-year = 1962

| year = 1927

| publisher = Plaza Publishing

| location = Salt Lake City, Utah

| isbn = 978-99929-4-881-1

| page = 442}}Any Shot You Want, The A-Square Handloading Manual, pg 604{{cite book

| last = Ackley

| first = P.O.

| title = Handbook for Shooters & Reloaders

| edition = 8th Printing

| series = vol II

| orig-year = 1966

| year = 1979

| publisher = Plaza Publishing

| location = Salt Lake City, Utah

| asin=B000BGII48

| page = 141}}Any Shot You Want, The A-Square Handloading Manual, pg 561 Some .378-based derivatives have gone on to be part of the Weatherby line: namely, the .30-378, .338-378, .416 and .460.{{Cite web |url=http://www.weatherby.com/products/ammunition.asp/ |title=Weatherby Ammunition |access-date=2007-04-01 |archive-url=https://web.archive.org/web/20070410164034/http://www.weatherby.com/products/ammunition.asp |archive-date=2007-04-10 |url-status=dead }}