Rifle · CIP · SAAMI (not in current Z299)
.30-378 Weatherby Magnum
Weatherby's ultra-magnum overbore cartridge combining .30 caliber bullets with the .378 Weatherby case.
- Caliber
- 0.308″ · 7.823 mm
- Introduced
- 1996
- Case
- Belted
- Parent
- .378 Weatherby Magnum
- Primary use
- Hunting
- Status
- Active
- Introduced
- 1996
- Type
- Rifle
- Origin
- United States
- Inventor
- Roy Weatherby
- Manufacturer
- Weatherby
- Standard
- CIP · SAAMI (not in current Z299)
- Status
- Active
- Availability
- Specialty
- Case capacity
- 131 gr H₂O
- Twist (typical)
- 1:10
- Primer
- Boxer Large Rifle
- Case type
- Belted
- Max pressure
- 63,817 psi, CIP transducer
- Eff. range
- 800 yd
- Max range
- 6300 yd
- Recoil
- 35–50 ft·lb
Introduced by Weatherby
Ballistics
Published velocity/energy data isn't available for .30-378 Weatherby Magnum. Parent case: .378 Weatherby Magnum.
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 ⌀ | 7.82 | 0.308 | ✓ |
| Neck ⌀ | 8.56 | 0.337 | ✓ |
| Shoulder ⌀ | 14.25 | 0.561 | ✓ |
| Shoulder angle | 25° | — | |
| Base ⌀ | 14.78 | 0.582 | ✓ |
| Rim ⌀ | 14.71 | 0.579 | ✓ |
| Belt ⌀ | 15.34 | 0.604 | ✓ |
| Rim thickness | 1.60 | 0.063 | ✓ |
| Neck length | 8.74 | 0.344 | ≈ |
| Case length | 73.99 | 2.913 | ✓ |
| Overall length | 92.66 | 3.648 | ~ |
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. .30-378 Weatherby Magnum is highlighted below.
Missing a dimension for .30-378 Weatherby Magnum? Some case measurements aren't in a published SAAMI/CIP drawing yet. Have a factory or reamer print? Send it → — verified hard-to-find data earns a free Lindcott sticker.
Factory loads
Being verified
Advertised FPS, energy, and BC are withheld until loads clear verification.
Suitable powders
9 reloading powders listed for .30-378 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 .30-378 Weatherby Magnum
Lineage
Connected reference
History
Developed by Weatherby in the 1990s by necking a .378 Weatherby Magnum case down to .30 caliber. Produces extreme velocities exceeding 3,400 fps with 180-grain bullets. Commercially released in 1996. Known for extreme barrel erosion due to overbore capacity. Appeals to long-range hunters seeking maximum flat trajectory.
FAQs
- What twist rate does .30-378 Weatherby Magnum use?
- .30-378 Weatherby Magnum typically uses a 1:10 twist rate.
- What bullet diameter is .30-378 Weatherby Magnum?
- .30-378 Weatherby Magnum uses a 0.308″ (7.823 mm) diameter bullet.
- Is .30-378 Weatherby Magnum still in production?
- .30-378 Weatherby Magnum is active; typical availability is specialty.
- What is .30-378 Weatherby Magnum used for?
- .30-378 Weatherby Magnum is primarily used for hunting.
- What is .30-378 Weatherby Magnum based on?
- .30-378 Weatherby Magnum is derived from the .378 Weatherby Magnum case.
- What are the best powders for .30-378 Weatherby Magnum?
- Reloading powders commonly listed for .30-378 Weatherby Magnum include Norma MRP, N570, 780, H1000, among 9 suitable options.
Sources & provenance
- Standard SAAMI — SAAMI cartridge & chamber drawing — .30-378 Weatherby Magnum
- Standard SAAMI — ANSI/SAAMI Z299 — Cartridge & Chamber Drawings archived
- Manufacturer .30-378 Weatherby Magnum — Wikipedia, citing Barnes 'Cartridges of the World' 13ed + Layne Simpson, Rifle Shooter (Jan 2011) · parent_cartridge
- Manufacturer Nosler — 30 Caliber 210gr AccuBond Long Range (100ct) — component bullet spec · representative_gun, grain_ballistics archived
- Manufacturer Behind the Bullet: The .30-378 Weatherby Magnum — American Hunter (NRA) · parent_cartridge
- Manufacturer Nosler — 30-378 Wby Mag 210gr AccuBond Long Range Trophy Grade Ammunition (SKU 60133) · grain_ballistics, representative_gun archived
- Manufacturer Weatherby — Weatherby Ballistics Specifications Chart (PDF) · grain_ballistics, representative_gun
Data & sources. Specs compiled from the Lindcott Armory reference; availability counted from 21 live factory loads; the trajectory is modeled (point-mass), not measured. See methodology. Spotted an error? Report it →
