Load Specifications
Load data in caliber .257 Weath. Mag. with .257 | 120gr | Speer Grand Slam bullet and 67 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 ReloadSwiss RS 80.
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% | 56,333 psi | 88% | 3097 fps | 100% |
| Accurate 4350 | <<locked>> | 82% | 56,898 psi | 89% | 3123 fps | 100% |
| Accurate High Country | <<locked>> | 86% | 54,172 psi | 85% | 3199 fps | 99.4% |
| Accurate MAGPRO | <<locked>> | 88% | 55,056 psi | 86% | 3205 fps | 98.8% |
| ADI AR 2209 | <<locked>> | 88% | 57,696 psi | 90% | 3192 fps | 99.9% |
| ADI AR 2213 | <<locked>> | 90% | 55,970 psi | 88% | 3205 fps | 99.5% |
| ADI AR 2217 | <<locked>> | 98% | 54,186 psi | 85% | 3169 fps | 99.6% |
| ADI AR 2225ᴾ | <<locked>> | 100% | 52,591 psi | 82% | 3192 fps | 100% |
| Alliant Power Pro Varmint | <<locked>> | 86% | 54,201 psi | 85% | 3127 fps | 99.8% |
| Alliant Reloder-16 | <<locked>> | 84% | 57,725 psi | 90% | 3179 fps | 100% |
| Alliant Reloder-19 | <<locked>> | 88% | 57,363 psi | 90% | 3182 fps | 99.9% |
| Alliant Reloder-22 | <<locked>> | 90% | 56,333 psi | 88% | 3199 fps | 99.9% |
| Alliant Reloder-23 | <<locked>> | 90% | 54,288 psi | 85% | 3107 fps | 100% |
| Alliant Reloder-25 | <<locked>> | 94% | 54,172 psi | 85% | 3176 fps | 100% |
| Alliant Reloder-26 | <<locked>> | 86% | 54,549 psi | 85% | 3192 fps | 100% |
| Alliant Reloder-33ᴾ | <<locked>> | 100% | 55,651 psi | 87% | 3261 fps | 97.5% |
| Baschieri & Pellagri 109 | <<locked>> | 92% | 56,811 psi | 89% | 3159 fps | 97.8% |
| Bofors RP15 | <<locked>> | 92% | 55,521 psi | 87% | 3186 fps | 99.9% |
| Bofors RP30 | <<locked>> | 98% | 57,740 psi | 90% | 3248 fps | 99.9% |
| Bofors RP5 | <<locked>> | 90% | 56,333 psi | 88% | 3199 fps | 99.9% |
| Hodgdon H1000 | <<locked>> | 96% | 55,738 psi | 87% | 3196 fps | 99.9% |
| Hodgdon H4831 | <<locked>> | 88% | 55,187 psi | 86% | 3133 fps | 99% |
| Hodgdon H4831 SC | <<locked>> | 88% | 54,157 psi | 85% | 3114 fps | 98.9% |
| Hodgdon Hybrid 100V | <<locked>> | 84% | 54,520 psi | 85% | 3045 fps | 100% |
| Hodgdon Retumbo | <<locked>> | 96% | 56,739 psi | 89% | 3323 fps | 100% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 37,507 psi | 59% | 2008 fps | 100% |
| IMR 4350 | <<locked>> | 84% | 56,623 psi | 89% | 3110 fps | 100% |
| IMR 4831 | <<locked>> | 84% | 57,043 psi | 89% | 3110 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 88% | 55,883 psi | 88% | 3114 fps | 99.2% |
| IMR 7828 SSC | <<locked>> | 90% | 54,230 psi | 85% | 3186 fps | 99.4% |
| IMR 8133 Enduronᴾ | <<locked>> | 100% | 48,167 psi | 75% | 3100 fps | 98.8% |
| Lovex S065 | <<locked>> | 82% | 56,782 psi | 89% | 3084 fps | 100% |
| Lovex S070 | <<locked>> | 82% | 55,376 psi | 87% | 3087 fps | 100% |
| Lovex S071 | <<locked>> | 96% | 57,653 psi | 90% | 3120 fps | 100% |
| Norma 204 | <<locked>> | 82% | 54,070 psi | 85% | 3110 fps | 99.7% |
| Norma 217ᴾ | <<locked>> | 100% | 48,747 psi | 76% | 3123 fps | 99.9% |
| Norma MRP | <<locked>> | 88% | 56,405 psi | 88% | 3222 fps | 100% |
| Norma URP | <<locked>> | 82% | 55,172 psi | 86% | 3104 fps | 100% |
| Ramshot Grand | <<locked>> | 90% | 55,042 psi | 86% | 3202 fps | 99.6% |
| Ramshot Hunter | <<locked>> | 82% | 54,027 psi | 85% | 3110 fps | 100% |
| Ramshot Magnum | <<locked>> | 94% | 57,653 psi | 90% | 3192 fps | 100% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 38,508 psi | 60% | 2054 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 82% | 57,072 psi | 89% | 3146 fps | 100% |
| ReloadSwiss RS 70 | <<locked>> | 82% | 55,521 psi | 87% | 3176 fps | 100% |
| ReloadSwiss RS 76 | <<locked>> | 94% | 53,563 psi | 84% | 3248 fps | 100% |
| ReloadSwiss RS 80 | <<locked>> | 98% | 57,290 psi | 90% | 3274 fps | 99.3% |
| Rottweil R 904 | <<locked>> | 86% | 54,882 psi | 86% | 3100 fps | 99.3% |
| Rottweil R 905 | <<locked>> | 88% | 57,014 psi | 89% | 3173 fps | 99.9% |
| Shooters World Long Rifle | <<locked>> | 82% | 56,782 psi | 89% | 3084 fps | 100% |
| Shooters World SW4350 | <<locked>> | 82% | 55,376 psi | 87% | 3087 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 82% | 55,767 psi | 87% | 3035 fps | 100% |
| SNPE Vectan Tubal 8000 | <<locked>> | 88% | 56,608 psi | 89% | 3166 fps | 99.9% |
| Somchem S361 | <<locked>> | 86% | 56,202 psi | 88% | 3087 fps | 99.1% |
| Somchem S365 | <<locked>> | 84% | 56,246 psi | 88% | 3107 fps | 100% |
| Somchem S385 | <<locked>> | 88% | 57,261 psi | 90% | 3136 fps | 100% |
| Vihtavuori N160 | <<locked>> | 82% | 56,637 psi | 89% | 3094 fps | 100% |
| Vihtavuori N165 | <<locked>> | 92% | 57,145 psi | 90% | 3120 fps | 100% |
| Vihtavuori N170 | <<locked>> | 96% | 56,159 psi | 88% | 3133 fps | 95.9% |
| Vihtavuori N550 | <<locked>> | 82% | 55,970 psi | 88% | 3100 fps | 100% |
| Vihtavuori N555 | <<locked>> | 88% | 56,159 psi | 88% | 3136 fps | 100% |
| Vihtavuori N560 | <<locked>> | 88% | 55,912 psi | 88% | 3219 fps | 99.2% |
| Vihtavuori N565 | <<locked>> | 94% | 56,347 psi | 88% | 3202 fps | 99.4% |
| Vihtavuori N568 | <<locked>> | 96% | 53,780 psi | 84% | 3205 fps | 98.3% |
| Vihtavuori N570 | <<locked>> | 98% | 54,737 psi | 86% | 3268 fps | 96.9% |
| Winchester 6.5 StaBALL | <<locked>> | 82% | 55,999 psi | 88% | 3038 fps | 100% |
| Winchester StaBALL HD | <<locked>> | 92% | 57,305 psi | 90% | 3251 fps | 100% |
| Winchester Supreme 780 | <<locked>> | 90% | 57,174 psi | 90% | 3133 fps | 99.9% |
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% | 40,248 psi | 63% | 2808 fps | 99.4% |
| Accurate 4350 | <<locked>> | 80% | 53,214 psi | 83% | 3068 fps | 100% |
| Accurate High Country | <<locked>> | 80% | 43,787 psi | 69% | 2992 fps | 97.5% |
| Accurate MAGPRO | <<locked>> | 80% | 41,524 psi | 65% | 2930 fps | 95.6% |
| ADI AR 2209 | <<locked>> | 80% | 44,222 psi | 69% | 2946 fps | 98.5% |
| ADI AR 2213 | <<locked>> | 80% | 39,537 psi | 62% | 2874 fps | 96.1% |
| ADI AR 2217 | <<locked>> | 86% | 36,071 psi | 57% | 2779 fps | 95.1% |
| ADI AR 2225 | <<locked>> | 84% | 30,632 psi | 48% | 2674 fps | 96% |
| Alliant Power Pro Varmint | <<locked>> | 80% | 44,614 psi | 70% | 2946 fps | 98.6% |
| Alliant Reloder-16 | <<locked>> | 80% | 50,807 psi | 80% | 3071 fps | 100% |
| Alliant Reloder-19 | <<locked>> | 80% | 44,193 psi | 69% | 2940 fps | 98.5% |
| Alliant Reloder-22 | <<locked>> | 80% | 40,118 psi | 63% | 2881 fps | 97.6% |
| Alliant Reloder-23 | <<locked>> | 80% | 38,783 psi | 61% | 2828 fps | 100% |
| Alliant Reloder-25 | <<locked>> | 80% | 33,605 psi | 53% | 2749 fps | 98.8% |
| Alliant Reloder-26 | <<locked>> | 80% | 43,482 psi | 68% | 2995 fps | 100% |
| Alliant Reloder-33 | <<locked>> | 96% | 47,776 psi | 75% | 3110 fps | 95.5% |
| Baschieri & Pellagri 109 | <<locked>> | 86% | 47,050 psi | 74% | 2972 fps | 95.4% |
| Bofors RP15 | <<locked>> | 80% | 37,231 psi | 58% | 2808 fps | 96.6% |
| Bofors RP30 | <<locked>> | 84% | 35,679 psi | 56% | 2795 fps | 95.3% |
| Bofors RP5 | <<locked>> | 80% | 40,118 psi | 63% | 2881 fps | 97.6% |
| Hodgdon H1000 | <<locked>> | 82% | 34,316 psi | 54% | 2733 fps | 95.1% |
| Hodgdon H4831 | <<locked>> | 80% | 42,192 psi | 66% | 2877 fps | 96.3% |
| Hodgdon H4831 SC | <<locked>> | 80% | 41,394 psi | 65% | 2861 fps | 96.1% |
| Hodgdon Hybrid 100V | <<locked>> | 80% | 47,776 psi | 75% | 2936 fps | 100% |
| Hodgdon Retumbo | 57.3 gr | 80% | 32,764 psi | 51% | 2772 fps | 95.6% |
| Hodgdon TrailBoss | <<locked>> | 80% | 28,137 psi | 44% | 1798 fps | 100% |
| IMR 4350 | <<locked>> | 80% | 49,951 psi | 78% | 2995 fps | 99.8% |
| IMR 4831 | <<locked>> | 80% | 50,169 psi | 79% | 3002 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 80% | 43,482 psi | 68% | 2874 fps | 96.9% |
| IMR 7828 SSC | <<locked>> | 80% | 38,189 psi | 60% | 2851 fps | 95.7% |
| IMR 8133 Enduron | <<locked>> | 92% | 36,550 psi | 57% | 2838 fps | 95.5% |
| Lovex S065 | <<locked>> | 80% | 53,345 psi | 84% | 3028 fps | 100% |
| Lovex S070 | <<locked>> | 80% | 51,793 psi | 81% | 3028 fps | 100% |
| Lovex S071 | <<locked>> | 80% | 34,664 psi | 54% | 2674 fps | 98.3% |
| Norma 204 | <<locked>> | 80% | 50,444 psi | 79% | 3045 fps | 99.3% |
| Norma 217 | <<locked>> | 88% | 32,053 psi | 50% | 2736 fps | 96% |
| Norma MRP | <<locked>> | 80% | 42,308 psi | 66% | 2956 fps | 99.2% |
| Norma URP | <<locked>> | 80% | 51,445 psi | 81% | 3045 fps | 100% |
| Ramshot Grand | <<locked>> | 80% | 37,898 psi | 59% | 2854 fps | 96.1% |
| Ramshot Hunter | <<locked>> | 80% | 50,459 psi | 79% | 3048 fps | 100% |
| Ramshot Magnum | <<locked>> | 80% | 34,040 psi | 53% | 2726 fps | 96.6% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 28,892 psi | 45% | 1841 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 80% | 53,258 psi | 83% | 3091 fps | 100% |
| ReloadSwiss RS 70 | <<locked>> | 80% | 51,663 psi | 81% | 3114 fps | 100% |
| ReloadSwiss RS 76 | 61.3 gr | 80% | 31,894 psi | 50% | 2743 fps | 96.5% |
| ReloadSwiss RS 80 | 69.5 gr | 90% | 42,061 psi | 66% | 2982 fps | 96% |
| Rottweil R 904 | <<locked>> | 80% | 45,252 psi | 71% | 2920 fps | 97.8% |
| Rottweil R 905 | <<locked>> | 80% | 43,569 psi | 68% | 2923 fps | 98.5% |
| Shooters World Long Rifle | <<locked>> | 80% | 53,345 psi | 84% | 3028 fps | 100% |
| Shooters World SW4350 | <<locked>> | 80% | 51,793 psi | 81% | 3028 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 80% | 52,359 psi | 82% | 2979 fps | 100% |
| SNPE Vectan Tubal 8000 | <<locked>> | 80% | 43,236 psi | 68% | 2917 fps | 98.4% |
| Somchem S361 | <<locked>> | 80% | 46,122 psi | 72% | 2904 fps | 97.4% |
| Somchem S365 | <<locked>> | 80% | 49,240 psi | 77% | 2999 fps | 100% |
| Somchem S385 | <<locked>> | 80% | 44,150 psi | 69% | 2900 fps | 99.1% |
| Vihtavuori N160 | <<locked>> | 80% | 53,098 psi | 83% | 3038 fps | 100% |
| Vihtavuori N165 | <<locked>> | 80% | 38,493 psi | 60% | 2766 fps | 97.7% |
| Vihtavuori N170 | <<locked>> | 94% | 52,417 psi | 82% | 3068 fps | 95% |
| Vihtavuori N550 | <<locked>> | 80% | 52,330 psi | 82% | 3041 fps | 100% |
| Vihtavuori N555 | <<locked>> | 80% | 43,192 psi | 68% | 2910 fps | 100% |
| Vihtavuori N560 | <<locked>> | 80% | 42,163 psi | 66% | 2946 fps | 96.5% |
| Vihtavuori N565 | <<locked>> | 82% | 37,521 psi | 59% | 2815 fps | 95.1% |
| Vihtavuori N568 | <<locked>> | 90% | 43,308 psi | 68% | 2995 fps | 95.8% |
| Vihtavuori N570 | <<locked>> | 96% | 50,850 psi | 80% | 3192 fps | 96% |
| Winchester 6.5 StaBALL | <<locked>> | 80% | 52,344 psi | 82% | 2982 fps | 100% |
| Winchester StaBALL HD | <<locked>> | 80% | 36,114 psi | 57% | 2877 fps | 100% |
| Winchester Supreme 780 | <<locked>> | 80% | 40,611 psi | 64% | 2825 fps | 97.7% |
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 67 powders for .257 Weath. Mag. loaded with the .257 | 120gr | Speer Grand Slam. Hodgdon Retumbo delivers the highest muzzle velocity at 3,323 fps; across all powders the maximum-charge window runs from 2,008 fps to 3,323 fps. ADI AR 2225 gives the best case fill at 100 %, and 67 of the 67 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 1:11.0 twist; slower twists will usually not stabilise this weight. ADI AR 2225, Alliant Reloder-33, 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. Hodgdon Retumbo, ReloadSwiss RS 76, ReloadSwiss RS 80 rank at the top here: for .257 Weath. Mag. with the .257 | 120gr | Speer Grand Slam 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.