Hunting construction
Soft-point, bonded, partitioned, and monolithic expanding bullets are designed differently. Their intended impact-velocity ranges and use cases come from the bullet or ammunition manufacturer.
THE CARTRIDGE LIBRARY · SPORTING & MATCH RIFLE
.257 Roberts
A .25-caliber sporting cartridge with standard and +P factory designations. The Roberts name records its wildcat-development heritage.
2A Ledger reference desk · Sources checked October 18, 2026
Read the dimensions
- Overall · min–max
- 2.620–2.780 in
66.548–70.612 mm - Case length · max
- 2.233 in
56.718 mm - Bullet maximum
- 0.258 in
6.553 mm - Rim diameter · max
- 0.473 in
12.014 mm
Know the exact name
At a glance
- Cartridge family
- Sporting & match rifle
- Bullet specification
- 0.2580 in / 6.553 mmBullet maximum
- Factory examples
- 1 loadsSelected, sourced examples below
- Weight in cited examples
- 117 grGrains measure mass, not powder charge
.257 Roberts is identified by its complete cartridge designation. The resource-table alternative is 257 Roberts. A caliber number, bullet diameter, or family resemblance on its own does not identify ammunition compatibility.
A +P marking identifies a separate pressure category; check the firearm maker's authorization. Ackley Improved is a separate chamber designation.
Dimensions: open the exact dimensional drawing ↗. The displayed number is bullet maximum, rather than an assertion that every manufactured projectile or barrel has this exact diameter.
Origins & evolution
Background & development
The .257 Roberts developed from experiments with the 7×57 Mauser case, with Ned Roberts as the central figure in a project that also involved other gunsmiths and experimenters. Early versions varied in shoulder shape, neck length and body taper. Remington adopted a commercial version in 1934, establishing the standardized .257 Roberts name.
That name helped distinguish the factory cartridge from the earlier .25 Roberts wildcats. The cartridge earned a strong sporting reputation, including praise from Townsend Whelen, but later competition from the .243 Winchester and .244/6 mm Remington drew attention away from it. Its history therefore bridges two periods: the era in which individual experimenters supplied major manufacturers with promising designs, and the later market dominated by mass-produced 6 mm sporting cartridges. The Roberts retained a loyal following because its original role as a moderate .25-caliber hunting cartridge remained useful even after newer introductions became more fashionable.
Historical sources: Sierra: .257 Roberts cartridge history ↗
Construction changes the story
Loads, variations & specialty offerings
Match construction
Open-tip match and tipped match bullets prioritize consistency and aerodynamics. A match designation does not by itself mean the projectile was designed for hunting expansion.
Specialty offerings
Lead-free, reduced-recoil, and premium long-range products are separate load designs when offered. Compare the exact SKU, bullet weight, test barrel, and intended role rather than relying on a cartridge-wide average.
In the cited .257 Roberts examples, bullet weights are 117 grains. These are the weights actually present in this source selection, not a claim that every possible loading is listed.
Bullet construction background: Hornady: anatomy of a bullet ↗. Exact product descriptions and velocities are cited in the factory table.
From the factory catalog
117 grains
2,946 fps
SST® · +P
Compare all 1 cited factory load records
| Maker / product | Bullet mass | Published construction | Muzzle velocity | Test barrel | Source |
|---|---|---|---|---|---|
| Hornady81353 | 117 gr 7.58 g | SST® +P | 2,946 fps 898 m/s | Not stated here; see source | Hornady · PDF p. 184 ↗ |
Explore the published data
Ballistics you can inspect
Select a legend entry to add or remove its line. Hover or tap a plotted point, or use the position slider. With the graph focused, arrow keys move the inspector. Solid dots identify source points; dashed connectors show estimates between them. Load construction, pressure category, and test setup can differ even at the same grain weight.
Read the original values as accessible tables
.257 Roberts: factory velocity downrange
| Exact load | Source | Published points |
|---|---|---|
| 117 gr Hornady SST® +P | Hornady | 0: 2946; 100: 2707; 200: 2480; 300: 2265; 400: 2060; 500: 1866 |
How to interpret the comparison
Changing bullet weight also often changes bullet design and propellant choice. Two curves are comparisons of the listed products, not a controlled experiment proving that bullet weight alone caused the difference. Catalog downrange points are projections under the maker’s conditions; barrel-study points are recorded observations in the study firearm.
Direct answers
Common questions
What is .257 Roberts?
A .25-caliber sporting cartridge with standard and +P factory designations. The Roberts name records its wildcat-development heritage.
What diameter does .257 Roberts use?
The cited dimensional standard lists 0.2580 inches (6.553 mm), bullet maximum. This drawing convention is different from a casual caliber nickname.
Are similarly named cartridges interchangeable?
A +P marking identifies a separate pressure category; check the firearm maker's authorization. Ackley Improved is a separate chamber designation.
Are the graph values measured or estimated?
The downrange view uses the exact manufacturer catalog records shown in the source table. Dashed connectors and intermediate inspector values use linear interpolation between the displayed source points. Calculated energy uses the listed bullet mass and velocity.
Does higher energy mean the best load?
Energy is calculated from mass and velocity. It does not establish accuracy, expansion, penetration, pattern density, recoil, or suitability for a particular firearm. Use the exact product documentation and firearm manual.
Trace the facts
Sources & methodology
Compiled by 2A Ledger from the linked standards, manufacturer publications, and identified test records. Checked October 18, 2026. Historical tests and older catalogs retain their original dates; a listing here does not establish current availability.
- SAAMI: dimensional drawing · PDF p. 94 ↗
- Sierra: .257 Roberts cartridge background ↗
- Hornady · PDF p. 184 ↗
Diameter figures preserve the cited drawing convention. Inch–millimeter conversion uses exactly 25.4 mm per inch. Factory specifications describe the maker’s test setup; your firearm, ammunition lot, temperature, and measuring method can produce different results. This is an educational factory-ammunition reference, not a reloading manual.