Load Specifications
Load data in caliber .256 Mag. Gibbs with .257 | 100gr | Barnes XLC BT bullet and 31 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 Somchem S365.
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 4350 | <<locked>> | 88% | 41,858 psi | 85% | 2900 fps | 96.7% |
| ADI AR 2208 | <<locked>> | 82% | 43,323 psi | 88% | 2854 fps | 97.6% |
| Alliant Reloder- TS 15.5 | <<locked>> | 82% | 43,439 psi | 88% | 2887 fps | 99% |
| Alliant Reloder-16 | <<locked>> | 90% | 42,931 psi | 87% | 2953 fps | 97.3% |
| Alliant Reloder-17 | <<locked>> | 86% | 43,192 psi | 88% | 2986 fps | 98.8% |
| Alliant Reloder-23ᴾ | <<locked>> | 100% | 42,670 psi | 87% | 2969 fps | 98.7% |
| Alliant Reloder-26 | <<locked>> | 98% | 44,498 psi | 90% | 3068 fps | 97.1% |
| Bofors RP3 | <<locked>> | 82% | 43,874 psi | 89% | 2904 fps | 99.1% |
| Hodgdon H380 | <<locked>> | 82% | 44,179 psi | 90% | 2897 fps | 96.8% |
| Hodgdon Hybrid 100V | <<locked>> | 92% | 42,699 psi | 87% | 2897 fps | 98.6% |
| Hodgdon LEVERevolution | <<locked>> | 82% | 44,570 psi | 90% | 2953 fps | 99.2% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 36,042 psi | 73% | 1932 fps | 100% |
| IMR 4064 | <<locked>> | 82% | 42,757 psi | 87% | 2838 fps | 97.8% |
| IMR 4831 | <<locked>> | 94% | 43,366 psi | 88% | 2917 fps | 97.3% |
| Norma URP | <<locked>> | 90% | 43,845 psi | 89% | 2946 fps | 97.2% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 36,593 psi | 74% | 1978 fps | 100% |
| ReloadSwiss RS 60 | <<locked>> | 84% | 42,728 psi | 87% | 2989 fps | 99.9% |
| ReloadSwiss RS 62 | <<locked>> | 90% | 43,947 psi | 89% | 2969 fps | 97% |
| ReloadSwiss RS 70 | <<locked>> | 90% | 43,323 psi | 88% | 2972 fps | 96.1% |
| Rottweil R 903 | <<locked>> | 84% | 43,947 psi | 89% | 2897 fps | 98.9% |
| SNPE Vectan SP 11 | <<locked>> | 84% | 44,570 psi | 90% | 2943 fps | 98.4% |
| SNPE Vectan Tubal 5000 | <<locked>> | 82% | 42,931 psi | 87% | 2769 fps | 100% |
| Somchem S355 | <<locked>> | 84% | 44,541 psi | 90% | 2900 fps | 98.9% |
| Somchem S365 | <<locked>> | 92% | 42,235 psi | 86% | 2956 fps | 99.5% |
| Unknown powder | <<locked>> | 88% | 44,454 psi | 90% | 2946 fps | 96.6% |
| Vihtavuori N150 | <<locked>> | 84% | 42,351 psi | 86% | 2825 fps | 99.4% |
| Vihtavuori N160 | <<locked>> | 88% | 42,902 psi | 87% | 2887 fps | 96.8% |
| Vihtavuori N550 | <<locked>> | 88% | 42,409 psi | 86% | 2890 fps | 96.5% |
| Vihtavuori N555 | <<locked>> | 98% | 44,135 psi | 90% | 2995 fps | 98% |
| Winchester 6.5 StaBALL | <<locked>> | 88% | 42,540 psi | 86% | 2858 fps | 98.8% |
| Winchester StaBALL HDᴾ | <<locked>> | 100% | 38,566 psi | 78% | 2969 fps | 98.6% |
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 4350 | <<locked>> | 84% | 36,666 psi | 74% | 2779 fps | 95% |
| ADI AR 2208 | <<locked>> | 80% | 40,944 psi | 83% | 2805 fps | 97.1% |
| Alliant Reloder- TS 15.5 | <<locked>> | 80% | 41,046 psi | 83% | 2835 fps | 98.5% |
| Alliant Reloder-16 | 40.7 gr | 86% | 38,232 psi | 78% | 2838 fps | 95.7% |
| Alliant Reloder-17 | <<locked>> | 80% | 35,621 psi | 72% | 2795 fps | 96.6% |
| Alliant Reloder-23 | <<locked>> | 92% | 33,852 psi | 69% | 2743 fps | 95.8% |
| Alliant Reloder-26 | 49.1 gr | 94% | 39,044 psi | 79% | 2936 fps | 95.1% |
| Bofors RP3 | <<locked>> | 80% | 41,162 psi | 83% | 2844 fps | 98.6% |
| Hodgdon H380 | <<locked>> | 80% | 41,510 psi | 84% | 2838 fps | 96% |
| Hodgdon Hybrid 100V | <<locked>> | 82% | 31,647 psi | 64% | 2625 fps | 95% |
| Hodgdon LEVERevolution | <<locked>> | 80% | 41,814 psi | 85% | 2894 fps | 98.8% |
| Hodgdon TrailBoss | <<locked>> | 80% | 26,963 psi | 55% | 1729 fps | 100% |
| IMR 4064 | <<locked>> | 80% | 40,132 psi | 81% | 2779 fps | 97.1% |
| IMR 4831 | <<locked>> | 88% | 36,332 psi | 74% | 2756 fps | 95% |
| Norma URP | <<locked>> | 86% | 38,870 psi | 79% | 2831 fps | 95.7% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 27,528 psi | 56% | 1775 fps | 100% |
| ReloadSwiss RS 60 | <<locked>> | 80% | 37,710 psi | 76% | 2867 fps | 99.4% |
| ReloadSwiss RS 62 | <<locked>> | 86% | 38,493 psi | 78% | 2848 fps | 95.3% |
| ReloadSwiss RS 70 | <<locked>> | 88% | 40,756 psi | 83% | 2910 fps | 95.2% |
| Rottweil R 903 | <<locked>> | 80% | 38,986 psi | 79% | 2789 fps | 97.9% |
| SNPE Vectan SP 11 | <<locked>> | 80% | 39,262 psi | 80% | 2828 fps | 97.2% |
| SNPE Vectan Tubal 5000 | <<locked>> | 80% | 40,480 psi | 82% | 2723 fps | 100% |
| Somchem S355 | <<locked>> | 80% | 39,508 psi | 80% | 2792 fps | 97.8% |
| Somchem S365 | 38.7 gr | 80% | 29,327 psi | 59% | 2612 fps | 95.5% |
| Unknown powder | <<locked>> | 84% | 39,204 psi | 80% | 2828 fps | 95% |
| Vihtavuori N150 | <<locked>> | 80% | 37,536 psi | 76% | 2720 fps | 98.5% |
| Vihtavuori N160 | <<locked>> | 84% | 37,797 psi | 77% | 2769 fps | 95.2% |
| Vihtavuori N550 | <<locked>> | 86% | 39,842 psi | 81% | 2831 fps | 95.7% |
| Vihtavuori N555 | <<locked>> | 90% | 34,548 psi | 70% | 2772 fps | 95% |
| Winchester 6.5 StaBALL | <<locked>> | 80% | 33,286 psi | 68% | 2631 fps | 96% |
| Winchester StaBALL HD | <<locked>> | 94% | 32,213 psi | 65% | 2766 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 62 powders for .256 Mag. Gibbs loaded with the .257 | 100gr | Barnes XLC BT. Alliant Reloder-26 delivers the highest muzzle velocity at 3,068 fps; across all powders the maximum-charge window runs from 1,932 fps to 3,068 fps. Alliant Reloder-23 gives the best case fill at 100 %, and 62 of the 62 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 100.0 gr projectile in 0.257" calls for a 1:10.0 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. Alliant Reloder-26, Alliant Reloder-16, Somchem S365 rank at the top here: for .256 Mag. Gibbs with the .257 | 100gr | Barnes XLC BT they combine a high case fill with complete burn and sit in the upper velocity band. As outliers, Accurate 2700, Alliant Reloder-19, Alliant Reloder-22 burn incompletely and react more sensitively to barrel length and temperature. Always begin at the start load and work up in small increments while checking case and primer for pressure signs.