Home › Browse Calibers › .338-57 O'Connor
Common uses: Hunting, Big Game
| Type | rifle (centerfire) |
| Typical load | 200gr reference load |
| Muzzle velocity | 2400 fps |
| Muzzle energy | 2550 ft-lb |
| Published G1 ballistic coefficient | 0.2 |
| Case length | 57 mm |
| Overall length | 78 mm |
| Range (yd) | Velocity (fps) | Energy (ft-lb) | Drop (in) |
|---|---|---|---|
| 0 | 2400 | 2558 | -1.5 |
| 100 | 1990 | 1759 | 0 |
| 200 | 1628 | 1176 | -7.4 |
| 300 | 1327 | 781 | -28.1 |
| 400 | 1112 | 549 | -68.8 |
| 500 | 985 | 431 | -137.5 |
A retained-energy reference only — not a shoot/don't-shoot distance. Real effective range depends on your accuracy, shot placement, bullet construction, and conditions. The ~1,000 ft-lb (deer-sized) and ~1,500 ft-lb (elk-sized) figures are commonly cited rules of thumb, not standards.
This reference load is not verified factory-load data; confirm the displayed inputs against a reliable published source where available, and verify modeled results with your own rifle.
The .338-57 O'Connor is a short, efficient medium-bore wildcat built on the compact 7x57 Mauser case, pairing a larger .338 bullet with modest velocity and correspondingly gentle recoil. Its intended niche is close-cover hunting of deer and black bear, where a heavy-for-caliber bullet at moderate speed favors deep penetration and brush-bucking over flat trajectory or long-range reach. It is a low-pressure, short-action-friendly concept rather than a magnum, and its ballistics fall off quickly past a couple hundred yards. In practice it remains an obscure curiosity: it requires custom dies, reamers, and reformed brass, and factory chamberings such as the .348 Winchester or 8mm Mauser cover much the same role without that effort. Its appeal is mainly to handloaders and wildcat enthusiasts drawn to a light-recoiling woods cartridge tied to O'Connor's name.
This wildcat originated with a proposal by gun writer Jack O'Connor to neck up the 7x57mm Mauser case to accept .338-inch bullets, creating a mild-recoiling cartridge for deer and black bear in timber. The concept was later named ".338x57 O'Connor" and developed in detail by Chuck Hawks, who published worked-out specifications for it. Jack O'Connor never built or standardized the finished cartridge himself, and it was never commercialized, so it exists essentially as a paper wildcat rather than a produced round.
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