Load Specifications
Load data in caliber .257 Ackley Improved with .257 | 90gr | Prvi Partizan HP bullet and 30 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are Somchem S365, Hodgdon Hybrid 100V and Winchester 6.5 StaBALL.
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% | 42,380 psi | 88% | 3022 fps | 100% |
| Accurate 4350 | <<locked>> | 90% | 41,394 psi | 86% | 3058 fps | 96.3% |
| ADI AR 2208 | <<locked>> | 82% | 41,147 psi | 85% | 2979 fps | 96.8% |
| Alliant Reloder- TS 15.5 | <<locked>> | 82% | 40,785 psi | 85% | 3002 fps | 98.2% |
| Alliant Reloder-16 | <<locked>> | 92% | 43,439 psi | 90% | 3133 fps | 97.1% |
| Alliant Reloder-17 | <<locked>> | 86% | 40,683 psi | 84% | 3094 fps | 98% |
| Alliant Reloder-23ᴾ | <<locked>> | 100% | 40,176 psi | 83% | 3071 fps | 97.8% |
| Bofors RP3 | <<locked>> | 84% | 43,482 psi | 90% | 3068 fps | 98.8% |
| Hodgdon Hybrid 100V | <<locked>> | 94% | 42,873 psi | 89% | 3068 fps | 98.4% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 35,404 psi | 73% | 2060 fps | 100% |
| IMR 4064 | <<locked>> | 82% | 43,250 psi | 90% | 3022 fps | 97.6% |
| IMR 4831 | <<locked>> | 92% | 42,380 psi | 88% | 3061 fps | 96.7% |
| Lovex S062 | <<locked>> | 82% | 43,236 psi | 90% | 3025 fps | 99% |
| Norma 203B | <<locked>> | 82% | 43,149 psi | 90% | 3061 fps | 98% |
| Norma URP | <<locked>> | 90% | 41,350 psi | 86% | 3054 fps | 96.1% |
| Ramshot Big Game | <<locked>> | 82% | 43,018 psi | 89% | 3071 fps | 97.8% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 35,766 psi | 74% | 2106 fps | 100% |
| ReloadSwiss RS 60 | <<locked>> | 86% | 43,337 psi | 90% | 3173 fps | 99.9% |
| Rottweil R 903 | <<locked>> | 86% | 43,613 psi | 90% | 3061 fps | 98.6% |
| Shooters World Precision | <<locked>> | 82% | 43,236 psi | 90% | 3025 fps | 99% |
| SNPE Vectan SP 11 | <<locked>> | 84% | 42,090 psi | 87% | 3061 fps | 97.6% |
| SNPE Vectan Tubal 5000 | <<locked>> | 84% | 43,294 psi | 90% | 2946 fps | 100% |
| Somchem S355 | <<locked>> | 84% | 41,524 psi | 86% | 3009 fps | 98% |
| Somchem S365 | <<locked>> | 94% | 42,235 psi | 88% | 3123 fps | 99.4% |
| Vihtavuori N150 | <<locked>> | 86% | 42,337 psi | 88% | 2992 fps | 99.2% |
| Vihtavuori N160 | <<locked>> | 90% | 43,221 psi | 90% | 3058 fps | 96.6% |
| Vihtavuori N550 | <<locked>> | 90% | 42,569 psi | 88% | 3058 fps | 96.2% |
| Vihtavuori N555 | <<locked>> | 98% | 41,307 psi | 86% | 3100 fps | 97% |
| Winchester 6.5 StaBALL | <<locked>> | 90% | 43,395 psi | 90% | 3035 fps | 98.7% |
| Winchester StaBALL HDᴾ | <<locked>> | 100% | 35,998 psi | 75% | 3051 fps | 97.2% |
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% | 39,769 psi | 83% | 2963 fps | 99.8% |
| Accurate 4350 | <<locked>> | 88% | 38,696 psi | 80% | 2995 fps | 95.4% |
| ADI AR 2208 | <<locked>> | 80% | 38,667 psi | 80% | 2917 fps | 96% |
| Alliant Reloder- TS 15.5 | <<locked>> | 80% | 38,261 psi | 79% | 2940 fps | 97.6% |
| Alliant Reloder-16 | <<locked>> | 88% | 38,363 psi | 80% | 3005 fps | 95.4% |
| Alliant Reloder-17 | <<locked>> | 80% | 33,098 psi | 69% | 2884 fps | 95% |
| Alliant Reloder-23 | <<locked>> | 94% | 33,170 psi | 69% | 2877 fps | 95% |
| Bofors RP3 | <<locked>> | 80% | 37,942 psi | 79% | 2940 fps | 97.6% |
| Hodgdon Hybrid 100V | 43.5 gr | 86% | 33,141 psi | 69% | 2825 fps | 95.3% |
| Hodgdon TrailBoss | <<locked>> | 80% | 26,397 psi | 55% | 1847 fps | 100% |
| IMR 4064 | <<locked>> | 80% | 40,611 psi | 84% | 2959 fps | 96.9% |
| IMR 4831 | <<locked>> | 88% | 37,275 psi | 77% | 2940 fps | 95% |
| Lovex S062 | <<locked>> | 80% | 40,364 psi | 84% | 2963 fps | 98.5% |
| Norma 203B | <<locked>> | 80% | 40,553 psi | 84% | 3002 fps | 97.3% |
| Norma URP | <<locked>> | 88% | 38,769 psi | 80% | 2995 fps | 95.3% |
| Ramshot Big Game | <<locked>> | 80% | 40,161 psi | 83% | 3009 fps | 97% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 26,789 psi | 56% | 1893 fps | 100% |
| ReloadSwiss RS 60 | <<locked>> | 80% | 35,230 psi | 73% | 2963 fps | 98.5% |
| Rottweil R 903 | <<locked>> | 80% | 35,679 psi | 74% | 2874 fps | 96.6% |
| Shooters World Precision | <<locked>> | 80% | 40,364 psi | 84% | 2963 fps | 98.5% |
| SNPE Vectan SP 11 | <<locked>> | 80% | 36,608 psi | 76% | 2927 fps | 95.9% |
| SNPE Vectan Tubal 5000 | <<locked>> | 80% | 38,072 psi | 79% | 2838 fps | 99.9% |
| Somchem S355 | <<locked>> | 80% | 36,608 psi | 76% | 2887 fps | 96.6% |
| Somchem S365 | 43.6 gr | 84% | 30,226 psi | 63% | 2799 fps | 95.5% |
| Vihtavuori N150 | <<locked>> | 80% | 34,708 psi | 72% | 2812 fps | 97.5% |
| Vihtavuori N160 | <<locked>> | 88% | 40,524 psi | 84% | 2999 fps | 95.8% |
| Vihtavuori N550 | <<locked>> | 88% | 39,958 psi | 83% | 2999 fps | 95.4% |
| Vihtavuori N555 | <<locked>> | 94% | 35,955 psi | 75% | 2966 fps | 95.1% |
| Winchester 6.5 StaBALL | 46.1 gr | 82% | 33,127 psi | 69% | 2779 fps | 95.5% |
| Winchester StaBALL HD | <<locked>> | 98% | 33,852 psi | 70% | 2979 fps | 96% |
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 | Prvi Partizan HP. ReloadSwiss RS 60 delivers the highest muzzle velocity at 3,173 fps; across all powders the maximum-charge window runs from 2,060 fps to 3,173 fps. Accurate 3100 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 72–90 %, 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. Accurate 3100, 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. Somchem S365, Hodgdon Hybrid 100V, Winchester 6.5 StaBALL rank at the top here: for .257 Ackley Improved with the .257 | 90gr | Prvi Partizan HP they combine a high case fill with complete burn and sit in the upper velocity band. As outliers, Accurate 3100, Bofors RP7, Hodgdon H414 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.