Load Specifications
Load data in caliber .257 Roberts with .257 | 100gr | Sierra SPT Pro-Hunter bullet and 47 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are Somchem S365, ReloadSwiss RS 70 and Alliant Reloder-17.
Important Notice: DO NOT go below Minimum Charge or above Maximum Charge. Since we have no control over the equipment and components used, any responsibility and liability for the results achieved is rejected.
Only powders/loads that match the current filter criteria are displayed: max pressure of a load ≤ 90% of max. standardized pressure, fill rate ≥ 80% and propellant combustion ≥ 95%. Use the sliders above the tables to adjust these thresholds.
Charge: Powder weight in grains. Start with the minimum load and work up carefully.
FR (Fill Rate): Case fill as a percentage. Values above 100% mean compressed loads.
MaxP / %: Maximum chamber pressure in bar and as a percentage of the standardized maximum for this caliber.
V(0): Muzzle velocity in feet per second (fps) at the standardized barrel length.
z (Powder Burn): Estimated propellant combustion percentage at bullet exit.
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Max Load - Barrel Length: 24"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| Accurate 2495 | <<locked>> | 82% | 44,846 psi | 87% | 2864 fps | 100% |
| Accurate 4064 | <<locked>> | 84% | 45,295 psi | 88% | 2913 fps | 100% |
| Accurate 4350 | <<locked>> | 92% | 44,208 psi | 86% | 2963 fps | 97.6% |
| ADI AR 2208 | <<locked>> | 86% | 46,557 psi | 90% | 2930 fps | 98.5% |
| Alliant Power Pro 2000-MR | <<locked>> | 82% | 44,454 psi | 86% | 3022 fps | 98.1% |
| Alliant Reloder- TS 15.5 | <<locked>> | 84% | 43,598 psi | 85% | 2900 fps | 99.1% |
| Alliant Reloder-15 | <<locked>> | 82% | 43,947 psi | 85% | 2917 fps | 98.1% |
| Alliant Reloder-16 | <<locked>> | 94% | 46,137 psi | 90% | 3031 fps | 98.3% |
| Alliant Reloder-17 | <<locked>> | 88% | 43,569 psi | 85% | 3005 fps | 99.1% |
| Alliant Reloder-23ᴾ | <<locked>> | 100% | 40,089 psi | 78% | 2920 fps | 98.3% |
| Alliant Reloder-26ᴾ | <<locked>> | 100% | 44,817 psi | 87% | 3084 fps | 97.5% |
| Bofors RP3 | <<locked>> | 84% | 43,569 psi | 85% | 2907 fps | 99.2% |
| Hodgdon H380 | <<locked>> | 84% | 44,266 psi | 86% | 2910 fps | 97% |
| Hodgdon Hybrid 100V | <<locked>> | 96% | 45,774 psi | 89% | 2969 fps | 99.3% |
| Hodgdon LEVERevolution | <<locked>> | 82% | 45,034 psi | 87% | 2969 fps | 99.4% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 35,447 psi | 69% | 1923 fps | 100% |
| IMR 4064 | <<locked>> | 84% | 46,122 psi | 90% | 2917 fps | 98.6% |
| IMR 4831 | <<locked>> | 94% | 45,310 psi | 88% | 2966 fps | 97.9% |
| IMR 4895 | <<locked>> | 82% | 45,020 psi | 87% | 2949 fps | 98.8% |
| Lovex S062 | <<locked>> | 84% | 46,079 psi | 89% | 2920 fps | 99.6% |
| Lovex S065 | <<locked>> | 90% | 45,426 psi | 88% | 2907 fps | 96.5% |
| Norma 203B | <<locked>> | 84% | 46,267 psi | 90% | 2963 fps | 99% |
| Norma URP | <<locked>> | 92% | 44,237 psi | 86% | 2963 fps | 97.5% |
| Ramshot Big Game | <<locked>> | 84% | 46,064 psi | 89% | 2976 fps | 98.8% |
| Ramshot Hunter | <<locked>> | 94% | 46,050 psi | 89% | 3002 fps | 96.2% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 35,868 psi | 70% | 1969 fps | 100% |
| ReloadSwiss RS 60 | <<locked>> | 88% | 46,412 psi | 90% | 3074 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 92% | 44,150 psi | 86% | 2982 fps | 97.3% |
| ReloadSwiss RS 70 | <<locked>> | 92% | 43,787 psi | 85% | 2992 fps | 96.6% |
| Rottweil R 902 | <<locked>> | 82% | 45,165 psi | 88% | 2881 fps | 99.5% |
| Rottweil R 903 | <<locked>> | 88% | 46,499 psi | 90% | 2959 fps | 99.4% |
| Shooters World Long Rifle | <<locked>> | 90% | 45,426 psi | 88% | 2907 fps | 96.5% |
| Shooters World Precision | <<locked>> | 84% | 46,079 psi | 89% | 2920 fps | 99.6% |
| SNPE Vectan SP 11 | <<locked>> | 86% | 45,020 psi | 87% | 2959 fps | 98.7% |
| SNPE Vectan Tubal 5000 | <<locked>> | 86% | 46,151 psi | 90% | 2835 fps | 100% |
| Somchem S355 | <<locked>> | 86% | 44,251 psi | 86% | 2907 fps | 99% |
| Somchem S365 | <<locked>> | 96% | 45,049 psi | 87% | 3022 fps | 99.9% |
| Unknown powder | <<locked>> | 90% | 44,991 psi | 87% | 2966 fps | 97% |
| Vihtavuori N135 | <<locked>> | 82% | 44,527 psi | 86% | 2858 fps | 100% |
| Vihtavuori N140 | <<locked>> | 82% | 45,397 psi | 88% | 2871 fps | 100% |
| Vihtavuori N150 | <<locked>> | 88% | 45,107 psi | 88% | 2887 fps | 99.8% |
| Vihtavuori N160 | <<locked>> | 92% | 46,021 psi | 89% | 2956 fps | 97.8% |
| Vihtavuori N540 | <<locked>> | 84% | 46,514 psi | 90% | 2910 fps | 100% |
| Vihtavuori N550 | <<locked>> | 92% | 45,382 psi | 88% | 2959 fps | 97.5% |
| Vihtavuori N555ᴾ | <<locked>> | 100% | 44,063 psi | 86% | 3005 fps | 98.2% |
| Winchester 6.5 StaBALL | <<locked>> | 92% | 46,137 psi | 90% | 2936 fps | 99.5% |
| Winchester StaBALL HDᴾ | <<locked>> | 100% | 35,911 psi | 70% | 2907 fps | 97.9% |
Recommended = one of the top powders for this cartridge and bullet combination.
Start Load - Barrel Length: 24"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| Accurate 2495 | <<locked>> | 80% | 42,105 psi | 82% | 2815 fps | 100% |
| Accurate 4064 | <<locked>> | 80% | 39,784 psi | 77% | 2805 fps | 100% |
| Accurate 4350 | <<locked>> | 86% | 35,868 psi | 70% | 2772 fps | 95% |
| ADI AR 2208 | <<locked>> | 80% | 38,682 psi | 75% | 2762 fps | 96.6% |
| Alliant Power Pro 2000-MR | <<locked>> | 80% | 41,553 psi | 81% | 2956 fps | 97.3% |
| Alliant Reloder- TS 15.5 | <<locked>> | 80% | 38,334 psi | 74% | 2785 fps | 98.1% |
| Alliant Reloder-15 | <<locked>> | 80% | 41,060 psi | 80% | 2851 fps | 97.5% |
| Alliant Reloder-16 | <<locked>> | 86% | 35,853 psi | 70% | 2785 fps | 95% |
| Alliant Reloder-17 | 40.6 gr | 80% | 33,112 psi | 64% | 2740 fps | 95.9% |
| Alliant Reloder-23 | <<locked>> | 94% | 33,127 psi | 64% | 2736 fps | 95.7% |
| Alliant Reloder-26 | <<locked>> | 96% | 39,044 psi | 76% | 2946 fps | 95.5% |
| Bofors RP3 | <<locked>> | 80% | 38,203 psi | 74% | 2792 fps | 98.2% |
| Hodgdon H380 | <<locked>> | 80% | 38,943 psi | 76% | 2792 fps | 95.5% |
| Hodgdon Hybrid 100V | <<locked>> | 84% | 30,937 psi | 60% | 2618 fps | 95% |
| Hodgdon LEVERevolution | <<locked>> | 80% | 42,119 psi | 82% | 2907 fps | 99% |
| Hodgdon TrailBoss | <<locked>> | 80% | 26,542 psi | 52% | 1726 fps | 100% |
| IMR 4064 | <<locked>> | 80% | 40,567 psi | 79% | 2799 fps | 97.4% |
| IMR 4831 | <<locked>> | 88% | 37,072 psi | 72% | 2789 fps | 95.6% |
| IMR 4895 | <<locked>> | 80% | 42,090 psi | 82% | 2887 fps | 98.3% |
| Lovex S062 | <<locked>> | 80% | 40,596 psi | 79% | 2808 fps | 98.9% |
| Lovex S065 | <<locked>> | 88% | 42,844 psi | 83% | 2851 fps | 95.8% |
| Norma 203B | <<locked>> | 80% | 40,451 psi | 79% | 2841 fps | 97.9% |
| Norma URP | <<locked>> | 86% | 36,187 psi | 70% | 2779 fps | 95% |
| Ramshot Big Game | <<locked>> | 80% | 40,292 psi | 78% | 2854 fps | 97.6% |
| Ramshot Hunter | <<locked>> | 92% | 43,105 psi | 84% | 2940 fps | 95.3% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 26,745 psi | 52% | 1762 fps | 100% |
| ReloadSwiss RS 60 | <<locked>> | 80% | 35,244 psi | 68% | 2815 fps | 99% |
| ReloadSwiss RS 62 | <<locked>> | 88% | 38,174 psi | 74% | 2851 fps | 95.5% |
| ReloadSwiss RS 70 | 46.4 gr | 90% | 41,002 psi | 80% | 2927 fps | 95.6% |
| Rottweil R 902 | <<locked>> | 80% | 42,279 psi | 82% | 2825 fps | 99.1% |
| Rottweil R 903 | <<locked>> | 80% | 35,752 psi | 69% | 2726 fps | 97.2% |
| Shooters World Long Rifle | <<locked>> | 88% | 42,844 psi | 83% | 2851 fps | 95.8% |
| Shooters World Precision | <<locked>> | 80% | 40,596 psi | 79% | 2808 fps | 98.9% |
| SNPE Vectan SP 11 | <<locked>> | 80% | 36,782 psi | 71% | 2779 fps | 96.7% |
| SNPE Vectan Tubal 5000 | <<locked>> | 80% | 38,087 psi | 74% | 2684 fps | 100% |
| Somchem S355 | <<locked>> | 80% | 36,637 psi | 71% | 2736 fps | 97.3% |
| Somchem S365 | 39.5 gr | 82% | 28,427 psi | 55% | 2602 fps | 95.3% |
| Unknown powder | <<locked>> | 86% | 39,276 psi | 76% | 2841 fps | 95.3% |
| Vihtavuori N135 | <<locked>> | 80% | 41,829 psi | 81% | 2812 fps | 100% |
| Vihtavuori N140 | <<locked>> | 80% | 42,438 psi | 82% | 2815 fps | 100% |
| Vihtavuori N150 | <<locked>> | 80% | 34,809 psi | 68% | 2667 fps | 98% |
| Vihtavuori N160 | <<locked>> | 86% | 37,695 psi | 73% | 2782 fps | 95.5% |
| Vihtavuori N540 | <<locked>> | 80% | 41,060 psi | 80% | 2805 fps | 99.9% |
| Vihtavuori N550 | <<locked>> | 86% | 37,173 psi | 72% | 2779 fps | 95.1% |
| Vihtavuori N555 | <<locked>> | 92% | 33,721 psi | 65% | 2762 fps | 95% |
| Winchester 6.5 StaBALL | <<locked>> | 80% | 30,966 psi | 60% | 2579 fps | 95.2% |
| Winchester StaBALL HD | <<locked>> | 96% | 31,517 psi | 61% | 2762 fps | 95.4% |
Recommended = one of the top powders for this cartridge and bullet combination.
ᴾ possible press load - work up slowly to this load while watching for signs of excessive pressure.
This overview compares 47 powders for .257 Roberts loaded with the .257 | 100gr | Sierra SPT Pro-Hunter. Alliant Reloder-26 delivers the highest muzzle velocity at 3,084 fps; across all powders the maximum-charge window runs from 1,923 fps to 3,084 fps. Alliant Reloder-23 gives the best case fill at 100 %, and 47 of the 47 powders fall inside the usable 80–100 % fill window.
Relative to the caliber's maximum pressure (355 MPa), the top charges use 69–90 %, leaving at least 10 % headroom. The 100.0 gr projectile in 0.257" calls for a 1:12.0 twist; slower twists will usually not stabilise this weight. Alliant Reloder-23, Alliant Reloder-26, Hodgdon TrailBoss reach 100 % fill or more at maximum charge, so these are compressed loads: they need a long drop tube to seat cleanly and react sensitively to the case capacity of your own brass lot. Somchem S365, ReloadSwiss RS 70, Alliant Reloder-17 rank at the top here: for .257 Roberts with the .257 | 100gr | Sierra SPT Pro-Hunter they combine a high case fill with complete burn and sit in the upper velocity band. Always begin at the start load and work up in small increments while checking case and primer for pressure signs.