Load Specifications
Load data in caliber .257 Roberts with .257 | 120gr | Speer Boat-Tail bullet and 50 powders. The key underlying parameters are shown in the table above.
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 3100 | <<locked>> | 98% | 44,744 psi | 87% | 2713 fps | 97.8% |
| Accurate 4350 | <<locked>> | 88% | 43,729 psi | 85% | 2713 fps | 98.9% |
| ADI AR 2208 | <<locked>> | 82% | 45,194 psi | 88% | 2667 fps | 99.4% |
| Alliant Reloder- TS 15.5 | <<locked>> | 82% | 45,411 psi | 88% | 2694 fps | 100% |
| Alliant Reloder-16 | <<locked>> | 90% | 45,440 psi | 88% | 2782 fps | 99.5% |
| Alliant Reloder-17 | <<locked>> | 86% | 45,411 psi | 88% | 2799 fps | 100% |
| Alliant Reloder-23ᴾ | <<locked>> | 100% | 45,034 psi | 87% | 2792 fps | 100% |
| Alliant Reloder-25ᴾ | <<locked>> | 100% | 39,610 psi | 77% | 2700 fps | 97.2% |
| Alliant Reloder-26 | <<locked>> | 96% | 44,208 psi | 86% | 2848 fps | 99% |
| Bofors RP3 | <<locked>> | 82% | 45,411 psi | 88% | 2700 fps | 100% |
| Bofors RP7 | <<locked>> | 86% | 45,629 psi | 89% | 2674 fps | 96.4% |
| Hodgdon H380 | <<locked>> | 82% | 46,296 psi | 90% | 2713 fps | 98.9% |
| Hodgdon H414 | <<locked>> | 88% | 46,224 psi | 90% | 2766 fps | 97.3% |
| Hodgdon H4350 | <<locked>> | 86% | 46,572 psi | 90% | 2726 fps | 95.9% |
| Hodgdon Hybrid 100V | <<locked>> | 92% | 45,150 psi | 88% | 2713 fps | 99.9% |
| Hodgdon Superformance | <<locked>> | 88% | 45,759 psi | 89% | 2789 fps | 96.7% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 36,013 psi | 70% | 1752 fps | 100% |
| IMR 4350 | <<locked>> | 90% | 46,195 psi | 90% | 2707 fps | 96.6% |
| IMR 4451 Enduron | <<locked>> | 84% | 44,614 psi | 87% | 2654 fps | 96.6% |
| IMR 4831 | <<locked>> | 90% | 44,817 psi | 87% | 2720 fps | 99.2% |
| Lovex S065 | <<locked>> | 86% | 44,367 psi | 86% | 2654 fps | 98% |
| Lovex S070 | <<locked>> | 88% | 45,208 psi | 88% | 2690 fps | 97.2% |
| Lovex S071ᴾ | <<locked>> | 100% | 39,755 psi | 77% | 2618 fps | 96.6% |
| Norma MRP | <<locked>> | 96% | 44,048 psi | 86% | 2805 fps | 96.6% |
| Norma URP | <<locked>> | 90% | 46,398 psi | 90% | 2766 fps | 99.3% |
| Ramshot Hunter | <<locked>> | 90% | 45,049 psi | 87% | 2753 fps | 97.8% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 36,593 psi | 71% | 1795 fps | 100% |
| ReloadSwiss RS 50 | <<locked>> | 82% | 46,427 psi | 90% | 2697 fps | 97.8% |
| ReloadSwiss RS 60 | <<locked>> | 84% | 45,324 psi | 88% | 2802 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 88% | 43,584 psi | 85% | 2736 fps | 98.7% |
| ReloadSwiss RS 70 | <<locked>> | 90% | 45,745 psi | 89% | 2812 fps | 98.9% |
| Rottweil R 903 | <<locked>> | 84% | 45,600 psi | 89% | 2697 fps | 99.9% |
| Rottweil R 905 | <<locked>> | 96% | 46,543 psi | 90% | 2776 fps | 95.8% |
| Rottweil R 907 | <<locked>> | 86% | 45,629 psi | 89% | 2674 fps | 96.4% |
| Shooters World Long Rifle | <<locked>> | 86% | 44,367 psi | 86% | 2654 fps | 98% |
| Shooters World SW4350 | <<locked>> | 88% | 45,208 psi | 88% | 2690 fps | 97.2% |
| SNPE Vectan SP 11 | <<locked>> | 82% | 44,034 psi | 86% | 2703 fps | 99.6% |
| SNPE Vectan Tubal 5000 | <<locked>> | 82% | 44,527 psi | 86% | 2562 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 86% | 43,918 psi | 85% | 2602 fps | 96.6% |
| Somchem S355 | <<locked>> | 84% | 46,137 psi | 90% | 2700 fps | 99.9% |
| Somchem S365 | <<locked>> | 92% | 44,976 psi | 87% | 2772 fps | 100% |
| Somchem S385 | <<locked>> | 94% | 44,353 psi | 86% | 2703 fps | 96.1% |
| Vihtavuori N150 | <<locked>> | 84% | 44,005 psi | 85% | 2628 fps | 100% |
| Vihtavuori N160 | <<locked>> | 88% | 45,194 psi | 88% | 2707 fps | 99% |
| Vihtavuori N165ᴾ | <<locked>> | 100% | 46,441 psi | 90% | 2730 fps | 96.2% |
| Vihtavuori N550 | <<locked>> | 88% | 44,512 psi | 86% | 2710 fps | 98.8% |
| Vihtavuori N555 | <<locked>> | 96% | 44,150 psi | 86% | 2766 fps | 99.4% |
| Winchester 6.5 StaBALL | <<locked>> | 88% | 44,614 psi | 87% | 2680 fps | 99.9% |
| Winchester 760 | <<locked>> | 88% | 46,224 psi | 90% | 2766 fps | 97.3% |
| Winchester StaBALL HDᴾ | <<locked>> | 100% | 40,379 psi | 78% | 2825 fps | 100% |
Start Load - Barrel Length: 24"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| Accurate 3100 | <<locked>> | 92% | 36,434 psi | 71% | 2549 fps | 95.5% |
| Accurate 4350 | <<locked>> | 80% | 33,286 psi | 65% | 2490 fps | 96.3% |
| ADI AR 2208 | <<locked>> | 80% | 42,511 psi | 83% | 2615 fps | 99% |
| Alliant Reloder- TS 15.5 | <<locked>> | 80% | 42,656 psi | 83% | 2641 fps | 99.8% |
| Alliant Reloder-16 | <<locked>> | 80% | 33,011 psi | 64% | 2497 fps | 96.3% |
| Alliant Reloder-17 | <<locked>> | 80% | 37,043 psi | 72% | 2625 fps | 99.1% |
| Alliant Reloder-23 | <<locked>> | 84% | 27,253 psi | 53% | 2359 fps | 95.2% |
| Alliant Reloder-25 | <<locked>> | 96% | 34,867 psi | 68% | 2582 fps | 95.2% |
| Alliant Reloder-26 | <<locked>> | 88% | 33,330 psi | 65% | 2592 fps | 95.6% |
| Bofors RP3 | <<locked>> | 80% | 42,612 psi | 83% | 2648 fps | 99.8% |
| Bofors RP7 | <<locked>> | 84% | 42,931 psi | 83% | 2621 fps | 95.7% |
| Hodgdon H380 | <<locked>> | 80% | 43,192 psi | 84% | 2654 fps | 98.4% |
| Hodgdon H414 | <<locked>> | 84% | 40,509 psi | 79% | 2651 fps | 95.7% |
| Hodgdon H4350 | <<locked>> | 84% | 43,830 psi | 85% | 2674 fps | 95.1% |
| Hodgdon Hybrid 100V | <<locked>> | 80% | 30,589 psi | 59% | 2402 fps | 97.1% |
| Hodgdon Superformance | <<locked>> | 86% | 42,424 psi | 82% | 2720 fps | 95.8% |
| Hodgdon TrailBoss | <<locked>> | 80% | 26,977 psi | 52% | 1568 fps | 100% |
| IMR 4350 | <<locked>> | 86% | 40,901 psi | 79% | 2602 fps | 95.1% |
| IMR 4451 Enduron | <<locked>> | 80% | 39,262 psi | 76% | 2546 fps | 95.1% |
| IMR 4831 | <<locked>> | 80% | 32,111 psi | 62% | 2444 fps | 95.9% |
| Lovex S065 | <<locked>> | 80% | 36,941 psi | 72% | 2500 fps | 96% |
| Lovex S070 | <<locked>> | 84% | 39,755 psi | 77% | 2579 fps | 95.7% |
| Lovex S071 | <<locked>> | 98% | 37,246 psi | 72% | 2566 fps | 95.8% |
| Norma MRP | <<locked>> | 94% | 41,089 psi | 80% | 2743 fps | 95.7% |
| Norma URP | <<locked>> | 80% | 33,402 psi | 65% | 2487 fps | 96.1% |
| Ramshot Hunter | <<locked>> | 84% | 36,912 psi | 72% | 2582 fps | 95.5% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 27,296 psi | 53% | 1604 fps | 100% |
| ReloadSwiss RS 50 | <<locked>> | 80% | 43,410 psi | 84% | 2638 fps | 97.1% |
| ReloadSwiss RS 60 | <<locked>> | 80% | 39,392 psi | 77% | 2687 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 80% | 32,996 psi | 64% | 2507 fps | 95.7% |
| ReloadSwiss RS 70 | <<locked>> | 82% | 34,795 psi | 68% | 2562 fps | 95.7% |
| Rottweil R 903 | <<locked>> | 80% | 40,147 psi | 78% | 2595 fps | 99.5% |
| Rottweil R 905 | <<locked>> | 94% | 43,671 psi | 85% | 2723 fps | 95% |
| Rottweil R 907 | <<locked>> | 84% | 42,931 psi | 83% | 2621 fps | 95.7% |
| Shooters World Long Rifle | <<locked>> | 80% | 36,941 psi | 72% | 2500 fps | 96% |
| Shooters World SW4350 | <<locked>> | 84% | 39,755 psi | 77% | 2579 fps | 95.7% |
| SNPE Vectan SP 11 | <<locked>> | 80% | 41,060 psi | 80% | 2644 fps | 99.2% |
| SNPE Vectan Tubal 5000 | <<locked>> | 80% | 42,076 psi | 82% | 2523 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 82% | 38,479 psi | 75% | 2493 fps | 95% |
| Somchem S355 | <<locked>> | 80% | 40,727 psi | 79% | 2598 fps | 99.5% |
| Somchem S365 | <<locked>> | 80% | 30,023 psi | 58% | 2444 fps | 98.3% |
| Somchem S385 | <<locked>> | 92% | 41,365 psi | 80% | 2648 fps | 95.2% |
| Vihtavuori N150 | <<locked>> | 80% | 38,798 psi | 75% | 2530 fps | 99.8% |
| Vihtavuori N160 | <<locked>> | 80% | 34,766 psi | 68% | 2490 fps | 96.6% |
| Vihtavuori N165 | <<locked>> | 98% | 43,598 psi | 85% | 2677 fps | 95.4% |
| Vihtavuori N550 | <<locked>> | 80% | 34,258 psi | 67% | 2490 fps | 96.2% |
| Vihtavuori N555 | <<locked>> | 84% | 29,588 psi | 57% | 2434 fps | 95.4% |
| Winchester 6.5 StaBALL | <<locked>> | 80% | 34,142 psi | 66% | 2464 fps | 98.5% |
| Winchester 760 | <<locked>> | 84% | 40,509 psi | 79% | 2651 fps | 95.7% |
| Winchester StaBALL HD | <<locked>> | 88% | 27,412 psi | 53% | 2444 fps | 96% |
ᴾ possible press load - work up slowly to this load while watching for signs of excessive pressure.
This overview compares 50 powders for .257 Roberts loaded with the .257 | 120gr | Speer Boat-Tail. Alliant Reloder-26 delivers the highest muzzle velocity at 2,848 fps; across all powders the maximum-charge window runs from 1,752 fps to 2,848 fps. Alliant Reloder-23 gives the best case fill at 100 %, and 50 of the 50 powders fall inside the usable 80–100 % fill window.
Relative to the caliber's maximum pressure (355 MPa), the top charges use 70–90 %, leaving at least 10 % headroom. The 120.0 gr projectile in 0.257" calls for a 1:10.5 twist; slower twists will usually not stabilise this weight. Alliant Reloder-23, Alliant Reloder-25, 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. Always begin at the start load and work up in small increments while checking case and primer for pressure signs.