Load Specifications
Load data in caliber .257 Weath. Mag. with .257 | 120gr | Sierra HPBT GameKing bullet and 64 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are Hodgdon Retumbo, ReloadSwiss RS 76 and Accurate MAGPRO.
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: 26"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| Accurate 3100 | <<locked>> | 90% | 55,825 psi | 87% | 3091 fps | 100% |
| Accurate 4350 | <<locked>> | 82% | 56,275 psi | 88% | 3114 fps | 100% |
| Accurate MAGPRO | <<locked>> | 90% | 55,419 psi | 87% | 3202 fps | 98.3% |
| ADI AR 2209 | <<locked>> | 88% | 57,159 psi | 90% | 3186 fps | 99.9% |
| ADI AR 2213 | <<locked>> | 90% | 55,463 psi | 87% | 3199 fps | 99.4% |
| ADI AR 2217ᴾ | <<locked>> | 100% | 57,609 psi | 90% | 3225 fps | 99.8% |
| ADI AR 2225ᴾ | <<locked>> | 100% | 51,924 psi | 81% | 3182 fps | 100% |
| Alliant Reloder-16 | <<locked>> | 84% | 57,421 psi | 90% | 3176 fps | 100% |
| Alliant Reloder-19 | <<locked>> | 88% | 56,884 psi | 89% | 3173 fps | 99.9% |
| Alliant Reloder-22 | <<locked>> | 90% | 55,840 psi | 88% | 3192 fps | 99.9% |
| Alliant Reloder-23 | <<locked>> | 92% | 57,450 psi | 90% | 3153 fps | 100% |
| Alliant Reloder-25 | <<locked>> | 96% | 57,435 psi | 90% | 3228 fps | 100% |
| Alliant Reloder-26 | <<locked>> | 86% | 54,012 psi | 85% | 3186 fps | 100% |
| Alliant Reloder-33ᴾ | <<locked>> | 100% | 54,969 psi | 86% | 3251 fps | 97.3% |
| Baschieri & Pellagri 109 | <<locked>> | 92% | 56,231 psi | 88% | 3150 fps | 97.6% |
| Bofors RP15 | <<locked>> | 92% | 55,042 psi | 86% | 3179 fps | 99.8% |
| Bofors RP30 | <<locked>> | 98% | 57,000 psi | 89% | 3238 fps | 99.8% |
| Bofors RP5 | <<locked>> | 90% | 55,840 psi | 88% | 3192 fps | 99.9% |
| Hodgdon H1000 | <<locked>> | 98% | 55,274 psi | 87% | 3186 fps | 99.9% |
| Hodgdon H4350 | <<locked>> | 82% | 55,085 psi | 86% | 3107 fps | 99.9% |
| Hodgdon H4831 | <<locked>> | 92% | 54,708 psi | 86% | 3123 fps | 98.9% |
| Hodgdon H4831 SC | <<locked>> | 90% | 57,609 psi | 90% | 3173 fps | 99.3% |
| Hodgdon Hybrid 100V | <<locked>> | 86% | 57,667 psi | 90% | 3091 fps | 100% |
| Hodgdon Retumbo | <<locked>> | 96% | 56,217 psi | 88% | 3314 fps | 100% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 37,463 psi | 59% | 2005 fps | 100% |
| IMR 4350 | <<locked>> | 84% | 56,115 psi | 88% | 3100 fps | 100% |
| IMR 4831 | <<locked>> | 86% | 54,708 psi | 86% | 3077 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 88% | 55,448 psi | 87% | 3107 fps | 99.1% |
| IMR 7828 SSC | <<locked>> | 90% | 57,537 psi | 90% | 3238 fps | 99.7% |
| IMR 8133 Enduronᴾ | <<locked>> | 100% | 47,471 psi | 74% | 3087 fps | 98.7% |
| Lovex S065 | <<locked>> | 82% | 56,507 psi | 89% | 3081 fps | 100% |
| Lovex S070 | <<locked>> | 82% | 54,839 psi | 86% | 3077 fps | 100% |
| Lovex S071 | <<locked>> | 96% | 57,145 psi | 90% | 3110 fps | 100% |
| Norma 204 | <<locked>> | 84% | 57,479 psi | 90% | 3166 fps | 99.9% |
| Norma 217ᴾ | <<locked>> | 100% | 48,225 psi | 76% | 3117 fps | 99.9% |
| Norma MRP | <<locked>> | 88% | 55,840 psi | 88% | 3212 fps | 100% |
| Norma URP | <<locked>> | 82% | 54,636 psi | 86% | 3097 fps | 100% |
| Ramshot Grand | <<locked>> | 88% | 57,711 psi | 90% | 3248 fps | 99.8% |
| Ramshot Hunter | <<locked>> | 84% | 57,305 psi | 90% | 3163 fps | 100% |
| Ramshot Magnum | <<locked>> | 90% | 54,911 psi | 86% | 3153 fps | 100% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 38,450 psi | 60% | 2051 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 82% | 56,521 psi | 89% | 3140 fps | 100% |
| ReloadSwiss RS 70 | <<locked>> | 82% | 54,998 psi | 86% | 3169 fps | 100% |
| ReloadSwiss RS 76 | <<locked>> | 96% | 57,232 psi | 90% | 3307 fps | 100% |
| ReloadSwiss RS 80 | <<locked>> | 98% | 56,536 psi | 89% | 3264 fps | 99.1% |
| Rottweil R 904 | <<locked>> | 86% | 54,404 psi | 85% | 3094 fps | 99.3% |
| Rottweil R 905 | <<locked>> | 88% | 56,521 psi | 89% | 3166 fps | 99.9% |
| Shooters World Long Rifle | <<locked>> | 82% | 56,507 psi | 89% | 3081 fps | 100% |
| Shooters World SW4350 | <<locked>> | 82% | 54,839 psi | 86% | 3077 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 82% | 55,550 psi | 87% | 3031 fps | 100% |
| SNPE Vectan Tubal 8000 | <<locked>> | 88% | 56,115 psi | 88% | 3159 fps | 99.9% |
| Somchem S361 | <<locked>> | 86% | 55,796 psi | 87% | 3081 fps | 99% |
| Somchem S365 | <<locked>> | 84% | 55,666 psi | 87% | 3097 fps | 100% |
| Somchem S385 | <<locked>> | 88% | 56,768 psi | 89% | 3130 fps | 100% |
| Vihtavuori N150 | <<locked>> | 84% | 57,406 psi | 90% | 3028 fps | 100% |
| Vihtavuori N165 | <<locked>> | 92% | 54,911 psi | 86% | 3084 fps | 99.9% |
| Vihtavuori N555 | <<locked>> | 88% | 55,883 psi | 88% | 3130 fps | 100% |
| Vihtavuori N560 | <<locked>> | 90% | 56,217 psi | 88% | 3228 fps | 99.3% |
| Vihtavuori N565 | <<locked>> | 94% | 55,898 psi | 88% | 3196 fps | 99.4% |
| Vihtavuori N568 | <<locked>> | 98% | 57,101 psi | 89% | 3264 fps | 98.8% |
| Vihtavuori N570 | <<locked>> | 98% | 54,737 psi | 86% | 3261 fps | 96.9% |
| Winchester 6.5 StaBALL | <<locked>> | 82% | 55,506 psi | 87% | 3031 fps | 100% |
| Winchester StaBALL HD | <<locked>> | 92% | 56,710 psi | 89% | 3245 fps | 100% |
| Winchester Supreme 780 | <<locked>> | 86% | 54,302 psi | 85% | 3087 fps | 99.8% |
Recommended = one of the top powders for this cartridge and bullet combination.
Start Load - Barrel Length: 26"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| Accurate 3100 | <<locked>> | 80% | 39,755 psi | 62% | 2799 fps | 99.3% |
| Accurate 4350 | <<locked>> | 80% | 52,634 psi | 82% | 3058 fps | 100% |
| Accurate MAGPRO | 63.1 gr | 84% | 44,831 psi | 70% | 2999 fps | 95.9% |
| ADI AR 2209 | <<locked>> | 80% | 43,729 psi | 69% | 2933 fps | 98.4% |
| ADI AR 2213 | <<locked>> | 80% | 39,088 psi | 61% | 2861 fps | 95.9% |
| ADI AR 2217 | <<locked>> | 88% | 38,189 psi | 60% | 2838 fps | 96% |
| ADI AR 2225 | <<locked>> | 84% | 30,458 psi | 48% | 2667 fps | 95.9% |
| Alliant Reloder-16 | <<locked>> | 80% | 50,227 psi | 79% | 3061 fps | 100% |
| Alliant Reloder-19 | <<locked>> | 80% | 43,729 psi | 69% | 2930 fps | 98.4% |
| Alliant Reloder-22 | <<locked>> | 80% | 39,653 psi | 62% | 2871 fps | 97.5% |
| Alliant Reloder-23 | <<locked>> | 80% | 38,493 psi | 60% | 2825 fps | 100% |
| Alliant Reloder-25 | <<locked>> | 80% | 33,199 psi | 52% | 2740 fps | 98.6% |
| Alliant Reloder-26 | <<locked>> | 80% | 43,207 psi | 68% | 2992 fps | 100% |
| Alliant Reloder-33 | <<locked>> | 96% | 47,340 psi | 74% | 3104 fps | 95.3% |
| Baschieri & Pellagri 109 | <<locked>> | 86% | 46,717 psi | 73% | 2966 fps | 95.3% |
| Bofors RP15 | <<locked>> | 80% | 36,970 psi | 58% | 2805 fps | 96.5% |
| Bofors RP30 | <<locked>> | 84% | 35,215 psi | 55% | 2785 fps | 95.1% |
| Bofors RP5 | <<locked>> | 80% | 39,653 psi | 62% | 2871 fps | 97.5% |
| Hodgdon H1000 | <<locked>> | 84% | 34,258 psi | 54% | 2733 fps | 95% |
| Hodgdon H4350 | <<locked>> | 80% | 51,692 psi | 81% | 3048 fps | 99.6% |
| Hodgdon H4831 | <<locked>> | 82% | 39,378 psi | 62% | 2815 fps | 95.3% |
| Hodgdon H4831 SC | <<locked>> | 80% | 40,944 psi | 64% | 2851 fps | 95.9% |
| Hodgdon Hybrid 100V | <<locked>> | 80% | 47,442 psi | 74% | 2930 fps | 100% |
| Hodgdon Retumbo | 56.8 gr | 80% | 32,372 psi | 51% | 2762 fps | 95.3% |
| Hodgdon TrailBoss | <<locked>> | 80% | 28,021 psi | 44% | 1791 fps | 100% |
| IMR 4350 | <<locked>> | 80% | 49,458 psi | 78% | 2986 fps | 99.7% |
| IMR 4831 | <<locked>> | 80% | 45,179 psi | 71% | 2910 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 80% | 43,062 psi | 67% | 2864 fps | 96.7% |
| IMR 7828 SSC | <<locked>> | 80% | 40,422 psi | 63% | 2907 fps | 96.5% |
| IMR 8133 Enduron | <<locked>> | 92% | 36,129 psi | 57% | 2831 fps | 95.3% |
| Lovex S065 | <<locked>> | 80% | 53,055 psi | 83% | 3025 fps | 100% |
| Lovex S070 | <<locked>> | 80% | 51,474 psi | 81% | 3022 fps | 100% |
| Lovex S071 | <<locked>> | 80% | 34,214 psi | 54% | 2664 fps | 98.1% |
| Norma 204 | <<locked>> | 80% | 50,212 psi | 79% | 3041 fps | 99.3% |
| Norma 217 | <<locked>> | 88% | 31,647 psi | 50% | 2726 fps | 95.8% |
| Norma MRP | <<locked>> | 80% | 42,032 psi | 66% | 2949 fps | 99.1% |
| Norma URP | <<locked>> | 80% | 51,155 psi | 80% | 3038 fps | 100% |
| Ramshot Grand | <<locked>> | 80% | 42,279 psi | 66% | 2959 fps | 97.5% |
| Ramshot Hunter | <<locked>> | 80% | 50,169 psi | 79% | 3045 fps | 100% |
| Ramshot Magnum | <<locked>> | 80% | 37,188 psi | 58% | 2808 fps | 97.7% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 28,776 psi | 45% | 1837 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 80% | 52,750 psi | 83% | 3081 fps | 100% |
| ReloadSwiss RS 70 | <<locked>> | 80% | 51,140 psi | 80% | 3107 fps | 100% |
| ReloadSwiss RS 76 | 60.8 gr | 80% | 31,517 psi | 49% | 2733 fps | 96.3% |
| ReloadSwiss RS 80 | <<locked>> | 90% | 41,626 psi | 65% | 2972 fps | 95.9% |
| Rottweil R 904 | <<locked>> | 80% | 44,773 psi | 70% | 2907 fps | 97.7% |
| Rottweil R 905 | <<locked>> | 80% | 43,279 psi | 68% | 2917 fps | 98.4% |
| Shooters World Long Rifle | <<locked>> | 80% | 53,055 psi | 83% | 3025 fps | 100% |
| Shooters World SW4350 | <<locked>> | 80% | 51,474 psi | 81% | 3022 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 80% | 51,851 psi | 81% | 2969 fps | 100% |
| SNPE Vectan Tubal 8000 | <<locked>> | 80% | 42,946 psi | 67% | 2913 fps | 98.3% |
| Somchem S361 | <<locked>> | 80% | 45,687 psi | 72% | 2897 fps | 97.2% |
| Somchem S365 | <<locked>> | 80% | 48,660 psi | 76% | 2989 fps | 100% |
| Somchem S385 | <<locked>> | 80% | 43,685 psi | 68% | 2890 fps | 99% |
| Vihtavuori N150 | <<locked>> | 80% | 50,662 psi | 79% | 2927 fps | 100% |
| Vihtavuori N165 | <<locked>> | 80% | 36,999 psi | 58% | 2733 fps | 97.2% |
| Vihtavuori N555 | <<locked>> | 80% | 42,844 psi | 67% | 2904 fps | 100% |
| Vihtavuori N560 | <<locked>> | 80% | 39,929 psi | 63% | 2897 fps | 95.7% |
| Vihtavuori N565 | <<locked>> | 84% | 39,813 psi | 62% | 2871 fps | 96% |
| Vihtavuori N568 | <<locked>> | 90% | 42,844 psi | 67% | 2986 fps | 95.6% |
| Vihtavuori N570 | <<locked>> | 96% | 50,821 psi | 80% | 3186 fps | 95.9% |
| Winchester 6.5 StaBALL | <<locked>> | 80% | 51,851 psi | 81% | 2976 fps | 100% |
| Winchester StaBALL HD | <<locked>> | 80% | 35,737 psi | 56% | 2871 fps | 100% |
| Winchester Supreme 780 | <<locked>> | 80% | 43,801 psi | 69% | 2894 fps | 98.4% |
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 64 powders for .257 Weath. Mag. loaded with the .257 | 120gr | Sierra HPBT GameKing. Hodgdon Retumbo delivers the highest muzzle velocity at 3,314 fps; across all powders the maximum-charge window runs from 2,005 fps to 3,314 fps. ADI AR 2217 gives the best case fill at 100 %, and 64 of the 64 powders fall inside the usable 80–100 % fill window.
Relative to the caliber's maximum pressure (440 MPa), the top charges use 59–90 %, leaving at least 10 % headroom. The 120.0 gr projectile in 0.257" calls for a 1:10.0 twist; slower twists will usually not stabilise this weight. ADI AR 2217, ADI AR 2225, Alliant Reloder-33 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. Hodgdon Retumbo, ReloadSwiss RS 76, Accurate MAGPRO rank at the top here: for .257 Weath. Mag. with the .257 | 120gr | Sierra HPBT 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.