Load Specifications
Load data in caliber .256 Mag. Gibbs with .257 | 117gr | Winchester SPRN bullet and 37 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are Alliant Reloder-26, Alliant Reloder-16 and ReloadSwiss RS 70.
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>> | 96% | 41,742 psi | 85% | 2703 fps | 96.8% |
| Accurate 4350 | <<locked>> | 88% | 43,787 psi | 89% | 2766 fps | 98.7% |
| Alliant Reloder-16 | <<locked>> | 88% | 42,540 psi | 86% | 2772 fps | 98.8% |
| Alliant Reloder-17 | <<locked>> | 84% | 42,598 psi | 86% | 2795 fps | 99.7% |
| Alliant Reloder-23 | <<locked>> | 98% | 42,148 psi | 85% | 2785 fps | 99.7% |
| Alliant Reloder-25ᴾ | <<locked>> | 100% | 39,610 psi | 80% | 2746 fps | 96.8% |
| Alliant Reloder-26 | <<locked>> | 96% | 44,309 psi | 90% | 2897 fps | 98.8% |
| Hodgdon H414 | <<locked>> | 86% | 43,105 psi | 87% | 2753 fps | 96.2% |
| Hodgdon Hybrid 100V | <<locked>> | 90% | 42,090 psi | 85% | 2710 fps | 99.6% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 36,158 psi | 73% | 1798 fps | 100% |
| IMR 4451 Enduron | <<locked>> | 84% | 44,570 psi | 90% | 2703 fps | 96.3% |
| IMR 4831 | <<locked>> | 88% | 41,785 psi | 85% | 2710 fps | 98.4% |
| Lovex S065 | <<locked>> | 86% | 44,295 psi | 90% | 2700 fps | 97.7% |
| Lovex S070 | <<locked>> | 86% | 42,395 psi | 86% | 2684 fps | 96.1% |
| Lovex S071ᴾ | <<locked>> | 100% | 39,740 psi | 81% | 2664 fps | 96.2% |
| Norma MRP | <<locked>> | 96% | 44,019 psi | 89% | 2851 fps | 96.3% |
| Norma URP | <<locked>> | 88% | 43,294 psi | 88% | 2756 fps | 98.6% |
| Ramshot Hunter | <<locked>> | 88% | 42,221 psi | 86% | 2746 fps | 96.8% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 36,695 psi | 74% | 1841 fps | 100% |
| ReloadSwiss RS 60 | <<locked>> | 82% | 42,076 psi | 85% | 2792 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 88% | 43,352 psi | 88% | 2782 fps | 98.4% |
| ReloadSwiss RS 70 | <<locked>> | 88% | 42,714 psi | 87% | 2795 fps | 98% |
| Rottweil R 903 | <<locked>> | 82% | 42,888 psi | 87% | 2697 fps | 99.7% |
| Shooters World Long Rifle | <<locked>> | 86% | 44,295 psi | 90% | 2700 fps | 97.7% |
| Shooters World SW4350 | <<locked>> | 86% | 42,395 psi | 86% | 2684 fps | 96.1% |
| SNPE Vectan SP 11 | <<locked>> | 82% | 43,903 psi | 89% | 2749 fps | 99.4% |
| SNPE Vectan Tubal 5000 | <<locked>> | 82% | 44,512 psi | 90% | 2615 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 86% | 43,729 psi | 89% | 2648 fps | 96.3% |
| Somchem S355 | <<locked>> | 82% | 43,178 psi | 88% | 2697 fps | 99.6% |
| Somchem S365 | <<locked>> | 90% | 41,756 psi | 85% | 2762 fps | 100% |
| Vihtavuori N150 | <<locked>> | 84% | 44,019 psi | 89% | 2677 fps | 100% |
| Vihtavuori N160 | <<locked>> | 86% | 42,250 psi | 86% | 2700 fps | 98.3% |
| Vihtavuori N550 | <<locked>> | 88% | 44,454 psi | 90% | 2756 fps | 98.6% |
| Vihtavuori N555 | <<locked>> | 96% | 44,121 psi | 89% | 2815 fps | 99.3% |
| Winchester 6.5 StaBALL | <<locked>> | 88% | 44,570 psi | 90% | 2726 fps | 99.9% |
| Winchester 760 | <<locked>> | 86% | 43,439 psi | 88% | 2759 fps | 96.2% |
| Winchester StaBALL HDᴾ | <<locked>> | 100% | 40,466 psi | 82% | 2874 fps | 100% |
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 3100 | <<locked>> | 92% | 36,260 psi | 74% | 2589 fps | 95% |
| Accurate 4350 | <<locked>> | 80% | 33,141 psi | 67% | 2530 fps | 95.8% |
| Alliant Reloder-16 | 37.8 gr | 80% | 33,011 psi | 67% | 2543 fps | 95.9% |
| Alliant Reloder-17 | <<locked>> | 80% | 36,985 psi | 75% | 2671 fps | 98.8% |
| Alliant Reloder-23 | <<locked>> | 86% | 28,935 psi | 59% | 2454 fps | 95.7% |
| Alliant Reloder-25 | <<locked>> | 98% | 37,115 psi | 75% | 2684 fps | 95.8% |
| Alliant Reloder-26 | 45.9 gr | 88% | 33,286 psi | 68% | 2631 fps | 95.1% |
| Hodgdon H414 | <<locked>> | 84% | 40,335 psi | 82% | 2697 fps | 95.3% |
| Hodgdon Hybrid 100V | <<locked>> | 80% | 30,560 psi | 62% | 2444 fps | 96.7% |
| Hodgdon TrailBoss | <<locked>> | 80% | 26,919 psi | 55% | 1604 fps | 100% |
| IMR 4451 Enduron | <<locked>> | 82% | 41,814 psi | 85% | 2648 fps | 95.5% |
| IMR 4831 | <<locked>> | 80% | 32,198 psi | 65% | 2490 fps | 95.5% |
| Lovex S065 | <<locked>> | 80% | 36,883 psi | 75% | 2543 fps | 95.6% |
| Lovex S070 | <<locked>> | 84% | 39,726 psi | 81% | 2625 fps | 95.3% |
| Lovex S071 | <<locked>> | 98% | 37,275 psi | 76% | 2608 fps | 95.4% |
| Norma MRP | <<locked>> | 94% | 41,147 psi | 83% | 2789 fps | 95.3% |
| Norma URP | <<locked>> | 80% | 33,344 psi | 68% | 2533 fps | 95.7% |
| Ramshot Hunter | <<locked>> | 84% | 37,028 psi | 75% | 2628 fps | 95.1% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 27,209 psi | 55% | 1640 fps | 100% |
| ReloadSwiss RS 60 | <<locked>> | 80% | 39,334 psi | 80% | 2733 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 80% | 32,938 psi | 67% | 2546 fps | 95.3% |
| ReloadSwiss RS 70 | 42.4 gr | 82% | 34,838 psi | 71% | 2608 fps | 95.3% |
| Rottweil R 903 | <<locked>> | 80% | 40,059 psi | 81% | 2641 fps | 99.3% |
| Shooters World Long Rifle | <<locked>> | 80% | 36,883 psi | 75% | 2543 fps | 95.6% |
| Shooters World SW4350 | <<locked>> | 84% | 39,726 psi | 81% | 2625 fps | 95.3% |
| SNPE Vectan SP 11 | <<locked>> | 80% | 41,075 psi | 83% | 2690 fps | 99% |
| SNPE Vectan Tubal 5000 | <<locked>> | 80% | 41,901 psi | 85% | 2569 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 84% | 40,886 psi | 83% | 2592 fps | 95.5% |
| Somchem S355 | <<locked>> | 80% | 40,683 psi | 83% | 2644 fps | 99.3% |
| Somchem S365 | <<locked>> | 80% | 29,907 psi | 61% | 2484 fps | 97.9% |
| Vihtavuori N150 | <<locked>> | 80% | 38,696 psi | 78% | 2575 fps | 99.7% |
| Vihtavuori N160 | <<locked>> | 80% | 34,635 psi | 70% | 2533 fps | 96.2% |
| Vihtavuori N550 | <<locked>> | 80% | 34,287 psi | 70% | 2536 fps | 95.8% |
| Vihtavuori N555 | <<locked>> | 84% | 29,617 psi | 60% | 2477 fps | 95% |
| Winchester 6.5 StaBALL | <<locked>> | 80% | 34,243 psi | 69% | 2510 fps | 98.2% |
| Winchester 760 | <<locked>> | 84% | 40,611 psi | 82% | 2700 fps | 95.4% |
| Winchester StaBALL HD | <<locked>> | 88% | 27,325 psi | 55% | 2474 fps | 95.2% |
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 37 powders for .256 Mag. Gibbs loaded with the .257 | 117gr | Winchester SPRN. Alliant Reloder-26 delivers the highest muzzle velocity at 2,897 fps; across all powders the maximum-charge window runs from 1,798 fps to 2,897 fps. Alliant Reloder-25 gives the best case fill at 100 %, and 37 of the 37 powders fall inside the usable 80–100 % fill window.
Relative to the caliber's maximum pressure (340 MPa), the top charges use 73–90 %, leaving at least 10 % headroom. The 117.0 gr projectile in 0.257" calls for a 1:12.5 twist; slower twists will usually not stabilise this weight. Alliant Reloder-25, Hodgdon TrailBoss, Lovex S071 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. Alliant Reloder-26, Alliant Reloder-16, ReloadSwiss RS 70 rank at the top here: for .256 Mag. Gibbs with the .257 | 117gr | Winchester SPRN 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.