Load Specifications
Load data in caliber .257 Ackley Improved with .257 | 90gr | Sierra GameKing bullet and 54 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are Alliant Reloder-16, Somchem S365 and Accurate 4350.
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 4064 | <<locked>> | 82% | 43,395 psi | 90% | 3045 fps | 100% |
| Accurate 4350 | <<locked>> | 90% | 42,583 psi | 88% | 3087 fps | 96.8% |
| Accurate 4350 | <<locked>> | 90% | 42,946 psi | 89% | 3097 fps | 96.9% |
| ADI AR 2208 | <<locked>> | 82% | 42,032 psi | 87% | 3005 fps | 97.2% |
| ADI AR 2208 | <<locked>> | 82% | 42,105 psi | 87% | 3009 fps | 97.2% |
| Alliant Reloder- TS 15.5 | <<locked>> | 82% | 41,945 psi | 87% | 3031 fps | 98.6% |
| Alliant Reloder- TS 15.5 | <<locked>> | 82% | 42,076 psi | 87% | 3035 fps | 98.6% |
| Alliant Reloder-16 | <<locked>> | 90% | 41,829 psi | 87% | 3100 fps | 96.8% |
| Alliant Reloder-16 | <<locked>> | 90% | 42,134 psi | 87% | 3110 fps | 97% |
| Alliant Reloder-17 | <<locked>> | 86% | 41,640 psi | 86% | 3123 fps | 98.4% |
| Alliant Reloder-17 | <<locked>> | 86% | 41,989 psi | 87% | 3133 fps | 98.5% |
| Alliant Reloder-23ᴾ | <<locked>> | 100% | 41,249 psi | 86% | 3104 fps | 98.2% |
| Alliant Reloder-23ᴾ | <<locked>> | 100% | 41,524 psi | 86% | 3114 fps | 98.4% |
| Alliant Reloder-26 | <<locked>> | 98% | 43,337 psi | 90% | 3212 fps | 96.6% |
| Bofors RP3 | <<locked>> | 82% | 41,655 psi | 86% | 3031 fps | 98.6% |
| Bofors RP3 | <<locked>> | 82% | 42,018 psi | 87% | 3041 fps | 98.7% |
| Hodgdon H380 | <<locked>> | 82% | 42,511 psi | 88% | 3035 fps | 96.2% |
| Hodgdon H380 | <<locked>> | 82% | 42,873 psi | 89% | 3048 fps | 96.3% |
| Hodgdon Hybrid 100V | <<locked>> | 92% | 41,234 psi | 86% | 3038 fps | 98.2% |
| Hodgdon Hybrid 100V | <<locked>> | 92% | 41,553 psi | 86% | 3045 fps | 98.3% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 35,563 psi | 74% | 2073 fps | 100% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 35,563 psi | 74% | 2077 fps | 100% |
| IMR 4831 | <<locked>> | 90% | 40,799 psi | 85% | 3031 fps | 96.4% |
| IMR 4831 | <<locked>> | 90% | 41,176 psi | 85% | 3041 fps | 96.5% |
| Norma URP | <<locked>> | 90% | 42,409 psi | 88% | 3084 fps | 96.6% |
| Norma URP | <<locked>> | 90% | 42,786 psi | 89% | 3094 fps | 96.8% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 35,911 psi | 75% | 2119 fps | 100% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 35,926 psi | 75% | 2123 fps | 100% |
| ReloadSwiss RS 60 | <<locked>> | 84% | 41,423 psi | 86% | 3136 fps | 99.8% |
| ReloadSwiss RS 60 | <<locked>> | 84% | 41,800 psi | 87% | 3146 fps | 99.8% |
| ReloadSwiss RS 62 | <<locked>> | 90% | 42,351 psi | 88% | 3104 fps | 96.4% |
| ReloadSwiss RS 62 | <<locked>> | 90% | 42,714 psi | 89% | 3114 fps | 96.5% |
| Rottweil R 903 | <<locked>> | 84% | 41,814 psi | 87% | 3028 fps | 98.4% |
| Rottweil R 903 | <<locked>> | 84% | 42,177 psi | 88% | 3038 fps | 98.5% |
| SNPE Vectan SP 11 | <<locked>> | 84% | 43,163 psi | 90% | 3087 fps | 98% |
| SNPE Vectan SP 11 | <<locked>> | 84% | 43,569 psi | 90% | 3097 fps | 98.1% |
| SNPE Vectan Tubal 5000 | <<locked>> | 82% | 41,481 psi | 86% | 2917 fps | 100% |
| SNPE Vectan Tubal 5000 | <<locked>> | 82% | 41,582 psi | 86% | 2920 fps | 100% |
| Somchem S355 | <<locked>> | 84% | 42,670 psi | 89% | 3038 fps | 98.4% |
| Somchem S355 | <<locked>> | 84% | 42,772 psi | 89% | 3041 fps | 98.4% |
| Somchem S365 | <<locked>> | 94% | 43,555 psi | 90% | 3156 fps | 99.6% |
| Somchem S365 | <<locked>> | 92% | 40,959 psi | 85% | 3100 fps | 99.3% |
| Vihtavuori N150 | <<locked>> | 86% | 43,410 psi | 90% | 3022 fps | 99.4% |
| Vihtavuori N150 | <<locked>> | 84% | 40,901 psi | 85% | 2969 fps | 99.1% |
| Vihtavuori N160 | <<locked>> | 88% | 41,568 psi | 86% | 3028 fps | 96.3% |
| Vihtavuori N160 | <<locked>> | 88% | 41,698 psi | 87% | 3031 fps | 96.4% |
| Vihtavuori N550 | <<locked>> | 88% | 40,959 psi | 85% | 3025 fps | 95.9% |
| Vihtavuori N550 | <<locked>> | 88% | 41,307 psi | 86% | 3035 fps | 96.1% |
| Vihtavuori N555 | <<locked>> | 98% | 42,656 psi | 88% | 3133 fps | 97.5% |
| Vihtavuori N555 | <<locked>> | 98% | 43,018 psi | 89% | 3140 fps | 97.6% |
| Winchester 6.5 StaBALL | <<locked>> | 88% | 41,379 psi | 86% | 2999 fps | 98.4% |
| Winchester 6.5 StaBALL | <<locked>> | 88% | 41,640 psi | 86% | 3009 fps | 98.5% |
| Winchester StaBALL HDᴾ | <<locked>> | 100% | 37,115 psi | 77% | 3094 fps | 98% |
| Winchester StaBALL HDᴾ | <<locked>> | 100% | 37,304 psi | 77% | 3104 fps | 98.1% |
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 4064 | <<locked>> | 80% | 40,756 psi | 85% | 2992 fps | 99.9% |
| Accurate 4350 | 47.2 gr | 88% | 39,813 psi | 83% | 3025 fps | 95.9% |
| Accurate 4350 | 46.2 gr | 86% | 37,420 psi | 78% | 2966 fps | 95.1% |
| ADI AR 2208 | <<locked>> | 80% | 39,262 psi | 81% | 2940 fps | 96.4% |
| ADI AR 2208 | <<locked>> | 80% | 39,610 psi | 82% | 2949 fps | 96.5% |
| Alliant Reloder- TS 15.5 | <<locked>> | 80% | 39,160 psi | 81% | 2969 fps | 97.9% |
| Alliant Reloder- TS 15.5 | <<locked>> | 80% | 39,305 psi | 82% | 2972 fps | 98% |
| Alliant Reloder-16 | 46 gr | 88% | 39,102 psi | 81% | 3031 fps | 95.8% |
| Alliant Reloder-16 | 45 gr | 86% | 37,072 psi | 77% | 2979 fps | 95% |
| Alliant Reloder-17 | <<locked>> | 80% | 33,982 psi | 71% | 2913 fps | 95.6% |
| Alliant Reloder-17 | <<locked>> | 80% | 34,113 psi | 71% | 2920 fps | 95.8% |
| Alliant Reloder-23 | <<locked>> | 94% | 34,171 psi | 71% | 2913 fps | 95.7% |
| Alliant Reloder-23 | <<locked>> | 94% | 34,432 psi | 71% | 2923 fps | 95.9% |
| Alliant Reloder-26 | <<locked>> | 96% | 40,408 psi | 84% | 3136 fps | 95.5% |
| Bofors RP3 | <<locked>> | 80% | 39,117 psi | 81% | 2972 fps | 98% |
| Bofors RP3 | <<locked>> | 80% | 39,247 psi | 81% | 2979 fps | 98.1% |
| Hodgdon H380 | <<locked>> | 80% | 39,711 psi | 82% | 2972 fps | 95.3% |
| Hodgdon H380 | <<locked>> | 80% | 40,059 psi | 83% | 2979 fps | 95.4% |
| Hodgdon Hybrid 100V | <<locked>> | 86% | 33,881 psi | 70% | 2851 fps | 95.8% |
| Hodgdon Hybrid 100V | <<locked>> | 86% | 34,171 psi | 71% | 2861 fps | 95.9% |
| Hodgdon TrailBoss | <<locked>> | 80% | 26,455 psi | 55% | 1857 fps | 100% |
| Hodgdon TrailBoss | <<locked>> | 80% | 26,513 psi | 55% | 1860 fps | 100% |
| IMR 4831 | <<locked>> | 88% | 38,319 psi | 79% | 2972 fps | 95.5% |
| IMR 4831 | <<locked>> | 88% | 38,435 psi | 80% | 2976 fps | 95.6% |
| Norma URP | <<locked>> | 88% | 39,827 psi | 83% | 3025 fps | 95.8% |
| Norma URP | <<locked>> | 86% | 37,463 psi | 78% | 2966 fps | 95% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 26,847 psi | 56% | 1903 fps | 100% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 26,919 psi | 56% | 1906 fps | 100% |
| ReloadSwiss RS 60 | <<locked>> | 80% | 36,187 psi | 75% | 2999 fps | 98.9% |
| ReloadSwiss RS 60 | <<locked>> | 80% | 36,274 psi | 75% | 3002 fps | 98.9% |
| ReloadSwiss RS 62 | <<locked>> | 88% | 39,479 psi | 82% | 3038 fps | 95.4% |
| ReloadSwiss RS 62 | <<locked>> | 88% | 39,842 psi | 83% | 3048 fps | 95.6% |
| Rottweil R 903 | <<locked>> | 80% | 36,564 psi | 76% | 2904 fps | 97% |
| Rottweil R 903 | <<locked>> | 80% | 36,941 psi | 77% | 2913 fps | 97.2% |
| SNPE Vectan SP 11 | <<locked>> | 80% | 37,666 psi | 78% | 2959 fps | 96.5% |
| SNPE Vectan SP 11 | <<locked>> | 80% | 37,797 psi | 78% | 2963 fps | 96.6% |
| SNPE Vectan Tubal 5000 | <<locked>> | 80% | 38,928 psi | 81% | 2861 fps | 100% |
| SNPE Vectan Tubal 5000 | <<locked>> | 80% | 39,088 psi | 81% | 2867 fps | 100% |
| Somchem S355 | <<locked>> | 80% | 37,478 psi | 78% | 2913 fps | 97.1% |
| Somchem S355 | <<locked>> | 80% | 37,608 psi | 78% | 2920 fps | 97.1% |
| Somchem S365 | 43.8 gr | 82% | 29,051 psi | 60% | 2766 fps | 95% |
| Somchem S365 | 43.8 gr | 82% | 29,341 psi | 61% | 2776 fps | 95.2% |
| Vihtavuori N150 | <<locked>> | 80% | 35,534 psi | 74% | 2841 fps | 97.9% |
| Vihtavuori N150 | <<locked>> | 80% | 35,882 psi | 74% | 2848 fps | 98% |
| Vihtavuori N160 | <<locked>> | 86% | 38,812 psi | 81% | 2963 fps | 95.4% |
| Vihtavuori N160 | <<locked>> | 86% | 39,146 psi | 81% | 2972 fps | 95.5% |
| Vihtavuori N550 | <<locked>> | 86% | 38,290 psi | 79% | 2963 fps | 95% |
| Vihtavuori N550 | <<locked>> | 86% | 38,595 psi | 80% | 2969 fps | 95.1% |
| Vihtavuori N555 | <<locked>> | 94% | 37,231 psi | 77% | 3002 fps | 95.8% |
| Vihtavuori N555 | <<locked>> | 94% | 37,565 psi | 78% | 3012 fps | 96% |
| Winchester 6.5 StaBALL | <<locked>> | 82% | 33,852 psi | 70% | 2808 fps | 96% |
| Winchester 6.5 StaBALL | <<locked>> | 80% | 31,778 psi | 66% | 2749 fps | 95.1% |
| Winchester StaBALL HD | <<locked>> | 96% | 32,460 psi | 67% | 2940 fps | 95.4% |
| Winchester StaBALL HD | <<locked>> | 96% | 32,692 psi | 68% | 2946 fps | 95.6% |
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 54 powders for .257 Ackley Improved loaded with the .257 | 90gr | Sierra GameKing. Alliant Reloder-26 delivers the highest muzzle velocity at 3,212 fps; across all powders the maximum-charge window runs from 2,073 fps to 3,212 fps. Alliant Reloder-23 gives the best case fill at 100 %, and 54 of the 54 powders fall inside the usable 80–100 % fill window.
Relative to the caliber's maximum pressure (332 MPa), the top charges use 74–90 %, leaving at least 10 % headroom. The 90.0 gr projectile in 0.257" calls for a 1:13.0 twist; slower twists will usually not stabilise this weight. Alliant Reloder-23, Alliant Reloder-23, 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-16, Somchem S365, Accurate 4350 rank at the top here: for .257 Ackley Improved with the .257 | 90gr | Sierra GameKing 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.