Rifle · SAAMI
.378 Weatherby Magnum
Roy Weatherby's .375-caliber belted magnum and the parent case for the .460 Weatherby.
- Caliber
- 0.375″ · 9.525 mm
- Introduced
- 1953
- Case
- Belted
- Parent
- .416 Rigby
- Primary use
- Hunting
- Status
- Active
- Introduced
- 1953
- Type
- Rifle
- Origin
- United States
- Inventor
- Roy Weatherby
- Manufacturer
- Weatherby
- Standard
- SAAMI
- Status
- Active
- Availability
- Specialty
- Case capacity
- 131 gr H₂O
- Twist (typical)
- 1:12
- Primer
- Large Rifle Magnum
- Case type
- Belted
- Max pressure
- 62,000 psi
- Eff. range
- 400 yd
- Max range
- 1000 yd
- Recoil
- 50–70 ft·lb
Introduced by Weatherby
Ballistics
Published velocity/energy data isn't available for .378 Weatherby Magnum. Parent case: .416 Rigby.
Performance
Dimensionscase measurements · scale drawing · size vs familiar rounds
Case dimensions — the scale drawing at the top of the page is built from these.
SAAMI · approximate| Measure | mm | in | ✓ |
|---|---|---|---|
| Bullet ⌀ | 9.53 | 0.375 | · |
| Neck ⌀ | 10.13 | 0.399 | · |
| Shoulder ⌀ | 14.22 | 0.560 | · |
| Shoulder angle | 22.2° | — | ~ |
| Base ⌀ | 14.78 | 0.582 | · |
| Rim ⌀ | 14.71 | 0.579 | · |
| Belt ⌀ | 15.32 | 0.603 | ~ |
| Rim thickness | 1.60 | 0.063 | · |
| Neck length | 9.40 | 0.370 | ≈ |
| Case length | 73.99 | 2.913 | ~ |
| Overall length | 92.71 | 3.650 | · |
Size vs familiar rounds
Drawn at true 1:1 — every case is accurate relative to the others. Absolute size depends on your screen's pixel density, so measuring one against a real ruler may be off. .378 Weatherby Magnum is highlighted below.
Factory loads
Being verified
Advertised FPS, energy, and BC are withheld until loads clear verification.
Suitable powders
12 reloading powders listed for .378 Weatherby Magnum, fastest to slowest. Cross-reference in the finder →
Reloading costestimate cost per round vs factory
Estimate your cost per round and how it compares to factory. Inputs are yours — nothing is stored.
Cost estimate only — not load data. Charge weight is your input; follow published manuals for safe charges.
Firearms chambered in .378 Weatherby Magnum
12 models in the database chamber .378 Weatherby Magnum. Browse all →
Lineage
Connected reference
History
Roy Weatherby introduced the .378 Wby Mag in 1953 on his proprietary large belted case. Weatherby's philosophy was maximum velocity at all calibers — the .378 pushes 300-grain bullets 300+ fps faster than .375 H&H, generating roughly 50% more muzzle energy. The .378 case became the parent for the .460 Weatherby Magnum, giving it outsized importance in Weatherby's cartridge lineage. Professional hunters in Africa used it for elephant and cape buffalo, though its recoil — often described as brutal even in heavy rifles — limited widespread adoption. Weatherby still manufactures ammunition and chambers the Mark V in .378.
FAQs
- What twist rate does .378 Weatherby Magnum use?
- .378 Weatherby Magnum typically uses a 1:12 twist rate.
- What bullet diameter is .378 Weatherby Magnum?
- .378 Weatherby Magnum uses a 0.375″ (9.525 mm) diameter bullet.
- Is .378 Weatherby Magnum still in production?
- .378 Weatherby Magnum is active; typical availability is specialty.
- What is .378 Weatherby Magnum used for?
- .378 Weatherby Magnum is primarily used for hunting.
- What is .378 Weatherby Magnum based on?
- .378 Weatherby Magnum is derived from the .416 Rigby case.
- What are the best powders for .378 Weatherby Magnum?
- Reloading powders commonly listed for .378 Weatherby Magnum include 203-B, Norma 204, Norma MRP, N170, among 12 suitable options.
Sources & provenance
- Standard SAAMI — SAAMI cartridge & chamber drawing — .378 Weatherby Magnum archived
- Standard SAAMI — ANSI/SAAMI Z299 — Cartridge & Chamber Drawings archived
- Manufacturer Weatherby, Inc. — Weatherby Ballistics Charts — 257 WBY MAG · grain_ballistics, representative_gun
- Manufacturer Choice Ammunition — .378 Weatherby Magnum 270 Grain Barnes TSX (Lead-Free) · grain_ballistics, representative_gun
- Manufacturer Choice Ammunition — .378 Weatherby Magnum 300 Grain Barnes TSX (Lead-Free) · grain_ballistics, representative_gun
Data & sources. Specs compiled from the Lindcott Armory reference; availability counted from 22 live factory loads; the trajectory is modeled (point-mass), not measured. See methodology. Spotted an error? Report it →