Home › Browse Calibers › .257 Rob. Imp.
Common uses: Hunting, Varmint
| Type | rifle (centerfire) |
| Typical load | 117gr Hornady Superformance SST |
| Muzzle velocity | 2946 fps |
| Muzzle energy | 2255 ft-lb |
| Published G1 ballistic coefficient | 0.39 |
| Case length | 57 mm |
| Overall length | 74.9 mm |
| Range (yd) | Velocity (fps) | Energy (ft-lb) | Drop (in) |
|---|---|---|---|
| 0 | 2946 | 2254 | -1.5 |
| 100 | 2703 | 1897 | 0 |
| 200 | 2473 | 1588 | -3.3 |
| 300 | 2254 | 1320 | -12.2 |
| 400 | 2046 | 1088 | -28.1 |
| 500 | 1851 | 890 | -52.3 |
At 1,000 yards, .257 Rob. Imp. (117gr at 2946 fps, 100 yd zero, standard conditions) has a modeled come-up of about 36.5 MOA / 10.6 MIL, retaining 1124 fps (transonic).
| Range (yd) | Velocity (fps) | State | Drop (in) | Elev (MOA) | Elev (MIL) |
|---|---|---|---|---|---|
| 300 | 2254 | Supersonic | -12.3 | 3.9 | 1.13 |
| 400 | 2046 | Supersonic | -28.1 | 6.7 | 1.95 |
| 500 | 1851 | Supersonic | -52.3 | 10.0 | 2.90 |
| 600 | 1668 | Supersonic | -86.7 | 13.8 | 4.01 |
| 700 | 1501 | Supersonic | -133.6 | 18.2 | 5.30 |
| 800 | 1352 | Supersonic | -196.0 | 23.4 | 6.81 |
| 900 | 1225 | Transonic | -277.5 | 29.5 | 8.57 |
| 1000 | 1124 | Transonic | -382.1 | 36.5 | 10.61 |
Extended predictions beyond 500 yards are modeled from the same G1 engine — useful for initial DOPE, but outside the 500-yard manufacturer-table validation audit. Confirm with observed DOPE, especially near transonic.
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.
Your barrel, ammunition lot, and conditions will differ — always verify against the manufacturer's data and your own rifle.
This is a handloader's cartridge that squeezes noticeably more velocity out of the .257 Roberts case without a large jump in recoil, making it a favorite among fans of the quarter-bore. With lighter bullets it serves well on varmints and predators, while heavier .25-caliber bullets around 115 to 120 grains make it a capable choice for deer, pronghorn, and similar medium game at moderate ranges. Its main appeal is efficiency and versatility: it delivers flat-shooting, mild-recoiling performance that suits smaller-framed shooters and lighter rifles. The practical trade-off is that it is a wildcat, so it depends on custom chambers, reloading, and fireforming from parent .257 Roberts brass rather than a supply of factory ammunition. Enthusiasts value it as a refined, well-balanced round rather than a long-range magnum.
The .257 Roberts Improved is a wildcat derived from the .257 Roberts, a quarter-bore cartridge that traces back to the 7×57mm Mauser and was commercialized by Remington in 1934. The "Improved" version applies P.O. Ackley's fireforming treatment to the parent case, sharpening the shoulder to roughly 40 degrees and reducing case body taper to increase powder capacity. Because an Improved chamber will safely fire and reform standard .257 Roberts factory ammunition, the wildcat gained a lasting following among handloaders seeking more performance from the classic Roberts case. Ackley himself wrote that the .257 Improved was a relatively efficient, flexible cartridge that came close to the mythical "all-around cartridge."
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