Load Specifications
Load data in caliber .257 Ackley Improved with .257 | 87gr | Speer MHP bullet and 33 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are Alliant Reloder-17, Somchem S365 and Hodgdon Hybrid 100V.
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 2495 | <<locked>> | 82% | 43,308 psi | 90% | 3048 fps | 100% |
| Accurate 4064 | <<locked>> | 84% | 43,540 psi | 90% | 3091 fps | 100% |
| Accurate 4350 | <<locked>> | 92% | 42,612 psi | 88% | 3127 fps | 96.2% |
| ADI AR 2208 | <<locked>> | 84% | 42,525 psi | 88% | 3048 fps | 96.7% |
| Alliant Power Pro 2000-MR | <<locked>> | 82% | 42,989 psi | 89% | 3189 fps | 96.6% |
| Alliant Reloder- TS 15.5 | <<locked>> | 84% | 42,279 psi | 88% | 3077 fps | 98.2% |
| Alliant Reloder-15 | <<locked>> | 82% | 42,424 psi | 88% | 3081 fps | 96.9% |
| Alliant Reloder-16 | <<locked>> | 92% | 42,105 psi | 87% | 3140 fps | 96.2% |
| Alliant Reloder-17 | <<locked>> | 88% | 42,163 psi | 87% | 3169 fps | 98% |
| Alliant Reloder-23ᴾ | <<locked>> | 100% | 38,638 psi | 80% | 3068 fps | 96.8% |
| Bofors RP3 | <<locked>> | 84% | 41,945 psi | 87% | 3074 fps | 98.2% |
| Hodgdon Hybrid 100V | <<locked>> | 94% | 41,408 psi | 86% | 3074 fps | 97.7% |
| Hodgdon LEVERevolution | <<locked>> | 82% | 43,323 psi | 90% | 3140 fps | 98.5% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 35,288 psi | 73% | 2090 fps | 100% |
| IMR 4064 | <<locked>> | 82% | 41,930 psi | 87% | 3028 fps | 96.8% |
| IMR 4895 | <<locked>> | 82% | 43,468 psi | 90% | 3120 fps | 97.7% |
| Lovex S062 | <<locked>> | 82% | 41,858 psi | 87% | 3035 fps | 98.5% |
| Norma 203B | <<locked>> | 82% | 41,742 psi | 87% | 3071 fps | 97.3% |
| Norma URP | <<locked>> | 92% | 42,554 psi | 88% | 3123 fps | 96% |
| Ramshot Big Game | <<locked>> | 82% | 41,582 psi | 86% | 3084 fps | 97.1% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 35,621 psi | 74% | 2136 fps | 100% |
| ReloadSwiss RS 60 | <<locked>> | 86% | 41,901 psi | 87% | 3179 fps | 99.6% |
| Rottweil R 903 | <<locked>> | 86% | 42,090 psi | 87% | 3071 fps | 98% |
| Shooters World Precision | <<locked>> | 82% | 41,858 psi | 87% | 3035 fps | 98.5% |
| SNPE Vectan SP 11 | <<locked>> | 84% | 40,669 psi | 84% | 3068 fps | 96.9% |
| SNPE Vectan Tubal 5000 | <<locked>> | 84% | 41,974 psi | 87% | 2963 fps | 100% |
| Somchem S355 | <<locked>> | 86% | 42,801 psi | 89% | 3077 fps | 98% |
| Somchem S365 | <<locked>> | 96% | 43,424 psi | 90% | 3192 fps | 99.3% |
| Vihtavuori N135 | <<locked>> | 82% | 43,062 psi | 89% | 3045 fps | 100% |
| Vihtavuori N150 | <<locked>> | 86% | 40,973 psi | 85% | 3002 fps | 98.7% |
| Vihtavuori N540 | <<locked>> | 82% | 42,250 psi | 88% | 3031 fps | 99.7% |
| Vihtavuori N555ᴾ | <<locked>> | 100% | 42,076 psi | 87% | 3156 fps | 96.8% |
| Winchester 6.5 StaBALL | <<locked>> | 90% | 41,887 psi | 87% | 3038 fps | 98% |
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 2495 | <<locked>> | 80% | 40,538 psi | 84% | 2992 fps | 100% |
| Accurate 4064 | <<locked>> | 80% | 38,290 psi | 79% | 2972 fps | 99.5% |
| Accurate 4350 | <<locked>> | 90% | 39,784 psi | 83% | 3058 fps | 95.3% |
| ADI AR 2208 | <<locked>> | 80% | 37,492 psi | 78% | 2927 fps | 95.1% |
| Alliant Power Pro 2000-MR | <<locked>> | 80% | 40,103 psi | 83% | 3114 fps | 95.6% |
| Alliant Reloder- TS 15.5 | <<locked>> | 80% | 36,999 psi | 77% | 2949 fps | 96.8% |
| Alliant Reloder-15 | <<locked>> | 80% | 39,827 psi | 83% | 3022 fps | 96.1% |
| Alliant Reloder-16 | <<locked>> | 90% | 39,566 psi | 82% | 3074 fps | 95.3% |
| Alliant Reloder-17 | 44.6 gr | 82% | 34,272 psi | 71% | 2953 fps | 95% |
| Alliant Reloder-23 | <<locked>> | 98% | 36,274 psi | 75% | 3002 fps | 95.9% |
| Bofors RP3 | <<locked>> | 80% | 36,579 psi | 76% | 2946 fps | 96.8% |
| Hodgdon Hybrid 100V | 44.1 gr | 88% | 33,895 psi | 70% | 2884 fps | 95.1% |
| Hodgdon LEVERevolution | <<locked>> | 80% | 40,364 psi | 84% | 3071 fps | 97.9% |
| Hodgdon TrailBoss | <<locked>> | 80% | 26,237 psi | 54% | 1873 fps | 100% |
| IMR 4064 | <<locked>> | 80% | 39,349 psi | 82% | 2969 fps | 96.1% |
| IMR 4895 | <<locked>> | 80% | 40,785 psi | 85% | 3058 fps | 97% |
| Lovex S062 | <<locked>> | 80% | 39,291 psi | 82% | 2976 fps | 97.9% |
| Norma 203B | <<locked>> | 80% | 39,204 psi | 81% | 3009 fps | 96.5% |
| Norma URP | <<locked>> | 90% | 39,871 psi | 83% | 3061 fps | 95.2% |
| Ramshot Big Game | <<locked>> | 80% | 38,783 psi | 80% | 3015 fps | 96.2% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 26,614 psi | 55% | 1919 fps | 100% |
| ReloadSwiss RS 60 | <<locked>> | 80% | 34,069 psi | 71% | 2966 fps | 97.6% |
| Rottweil R 903 | <<locked>> | 80% | 34,345 psi | 71% | 2877 fps | 95.6% |
| Shooters World Precision | <<locked>> | 80% | 39,291 psi | 82% | 2976 fps | 97.9% |
| SNPE Vectan SP 11 | <<locked>> | 80% | 35,360 psi | 73% | 2930 fps | 95% |
| SNPE Vectan Tubal 5000 | <<locked>> | 80% | 36,869 psi | 76% | 2851 fps | 99.7% |
| Somchem S355 | <<locked>> | 80% | 35,331 psi | 73% | 2894 fps | 95.7% |
| Somchem S365 | 44.4 gr | 86% | 31,270 psi | 65% | 2867 fps | 95.5% |
| Vihtavuori N135 | <<locked>> | 80% | 40,306 psi | 84% | 2989 fps | 100% |
| Vihtavuori N150 | <<locked>> | 80% | 33,504 psi | 70% | 2818 fps | 96.7% |
| Vihtavuori N540 | <<locked>> | 80% | 39,740 psi | 82% | 2972 fps | 99.5% |
| Vihtavuori N555 | <<locked>> | 96% | 36,840 psi | 76% | 3031 fps | 95% |
| Winchester 6.5 StaBALL | <<locked>> | 84% | 34,316 psi | 71% | 2848 fps | 95.5% |
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 33 powders for .257 Ackley Improved loaded with the .257 | 87gr | Speer MHP. Somchem S365 delivers the highest muzzle velocity at 3,192 fps; across all powders the maximum-charge window runs from 2,090 fps to 3,192 fps. Alliant Reloder-23 gives the best case fill at 100 %, and 33 of the 33 powders fall inside the usable 80–100 % fill window.
Relative to the caliber's maximum pressure (332 MPa), the top charges use 73–90 %, leaving at least 10 % headroom. The 87.0 gr projectile in 0.257" calls for a 1:12.0 twist; slower twists will usually not stabilise this weight. Alliant Reloder-23, Hodgdon TrailBoss, ReloadSwiss RS 14 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-17, Somchem S365, Hodgdon Hybrid 100V rank at the top here: for .257 Ackley Improved with the .257 | 87gr | Speer MHP 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.