Load Specifications
Load data in caliber .257 Weath. Mag. with .257 | 100gr | Impala RNFP KO bullet and 69 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are Winchester StaBALL HD, ReloadSwiss RS 76 and Hodgdon Retumbo.
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>> | 92% | 56,710 psi | 89% | 3330 fps | 100% |
| Accurate 4350 | <<locked>> | 84% | 57,348 psi | 90% | 3369 fps | 100% |
| Accurate MAGPRO | <<locked>> | 92% | 55,361 psi | 87% | 3422 fps | 96.6% |
| ADI AR 2209 | <<locked>> | 90% | 57,145 psi | 90% | 3415 fps | 99.2% |
| ADI AR 2213 | <<locked>> | 92% | 55,187 psi | 86% | 3415 fps | 98.2% |
| ADI AR 2217ᴾ | <<locked>> | 100% | 53,461 psi | 84% | 3366 fps | 98.2% |
| ADI AR 2225ᴾ | <<locked>> | 100% | 48,254 psi | 76% | 3327 fps | 99.6% |
| Alliant Reloder-16 | <<locked>> | 86% | 57,116 psi | 90% | 3422 fps | 100% |
| Alliant Reloder-19 | <<locked>> | 90% | 56,739 psi | 89% | 3402 fps | 99.2% |
| Alliant Reloder-22 | <<locked>> | 92% | 55,724 psi | 87% | 3422 fps | 99.2% |
| Alliant Reloder-23 | <<locked>> | 94% | 56,942 psi | 89% | 3392 fps | 100% |
| Alliant Reloder-25 | <<locked>> | 98% | 56,492 psi | 89% | 3458 fps | 100% |
| Alliant Reloder-26 | <<locked>> | 90% | 57,682 psi | 90% | 3491 fps | 100% |
| Bofors RP15 | <<locked>> | 94% | 54,911 psi | 86% | 3402 fps | 99% |
| Bofors RP30ᴾ | <<locked>> | 100% | 56,623 psi | 89% | 3458 fps | 98.9% |
| Bofors RP5 | <<locked>> | 92% | 55,724 psi | 87% | 3422 fps | 99.2% |
| Bofors RP7 | <<locked>> | 82% | 55,187 psi | 86% | 3301 fps | 99.5% |
| Hodgdon H1000ᴾ | <<locked>> | 100% | 54,853 psi | 86% | 3399 fps | 98.9% |
| Hodgdon H4350 | <<locked>> | 84% | 55,477 psi | 87% | 3343 fps | 99.1% |
| Hodgdon H4831 | <<locked>> | 94% | 54,621 psi | 86% | 3337 fps | 97.4% |
| Hodgdon H4831 SC | <<locked>> | 92% | 57,638 psi | 90% | 3392 fps | 98% |
| Hodgdon Hybrid 100V | <<locked>> | 86% | 54,244 psi | 85% | 3281 fps | 100% |
| Hodgdon Retumbo | <<locked>> | 98% | 55,230 psi | 87% | 3533 fps | 99.8% |
| Hodgdon Superformance | <<locked>> | 82% | 54,839 psi | 86% | 3386 fps | 99.6% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 37,463 psi | 59% | 2175 fps | 100% |
| IMR 4166 Enduron | <<locked>> | 82% | 57,537 psi | 90% | 3323 fps | 99.8% |
| IMR 4350 | <<locked>> | 86% | 56,652 psi | 89% | 3340 fps | 99.6% |
| IMR 4451 Enduron | <<locked>> | 82% | 55,941 psi | 88% | 3317 fps | 99.7% |
| IMR 4831 | <<locked>> | 88% | 55,216 psi | 87% | 3320 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 90% | 55,883 psi | 88% | 3330 fps | 97.8% |
| IMR 7828 SSC | <<locked>> | 92% | 56,942 psi | 89% | 3461 fps | 98.5% |
| IMR 8133 Enduronᴾ | <<locked>> | 100% | 44,048 psi | 69% | 3225 fps | 96% |
| Lovex S065 | <<locked>> | 84% | 57,421 psi | 90% | 3327 fps | 100% |
| Lovex S070 | <<locked>> | 84% | 55,724 psi | 87% | 3320 fps | 99.8% |
| Lovex S071 | <<locked>> | 98% | 57,682 psi | 90% | 3350 fps | 100% |
| Norma 204 | <<locked>> | 86% | 57,711 psi | 90% | 3396 fps | 99.1% |
| Norma 217ᴾ | <<locked>> | 100% | 44,454 psi | 70% | 3261 fps | 98.4% |
| Norma MRP | <<locked>> | 90% | 55,521 psi | 87% | 3445 fps | 99.8% |
| Norma URP | <<locked>> | 84% | 54,998 psi | 86% | 3340 fps | 100% |
| Ramshot Grand | <<locked>> | 90% | 57,014 psi | 89% | 3468 fps | 98.8% |
| Ramshot Hunter | <<locked>> | 86% | 57,508 psi | 90% | 3402 fps | 100% |
| Ramshot Magnum | <<locked>> | 92% | 54,491 psi | 85% | 3369 fps | 99.5% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 38,247 psi | 60% | 2224 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 84% | 56,898 psi | 89% | 3383 fps | 100% |
| ReloadSwiss RS 70 | <<locked>> | 84% | 54,897 psi | 86% | 3412 fps | 100% |
| ReloadSwiss RS 76 | <<locked>> | 98% | 56,275 psi | 88% | 3530 fps | 100% |
| ReloadSwiss RS 80ᴾ | <<locked>> | 100% | 55,782 psi | 87% | 3471 fps | 97.6% |
| Rottweil R 904 | <<locked>> | 88% | 54,679 psi | 86% | 3317 fps | 98% |
| Rottweil R 905 | <<locked>> | 90% | 56,724 psi | 89% | 3396 fps | 99.3% |
| Rottweil R 907 | <<locked>> | 82% | 55,187 psi | 86% | 3301 fps | 99.5% |
| Shooters World Long Rifle | <<locked>> | 84% | 57,421 psi | 90% | 3327 fps | 100% |
| Shooters World SW4350 | <<locked>> | 84% | 55,724 psi | 87% | 3320 fps | 99.8% |
| SNPE Vectan Tubal 7000 | <<locked>> | 84% | 56,536 psi | 89% | 3268 fps | 99.8% |
| SNPE Vectan Tubal 8000 | <<locked>> | 90% | 56,275 psi | 88% | 3389 fps | 99.2% |
| Somchem S361 | <<locked>> | 88% | 56,463 psi | 88% | 3304 fps | 97.8% |
| Somchem S365 | <<locked>> | 86% | 55,970 psi | 88% | 3353 fps | 100% |
| Somchem S385 | <<locked>> | 90% | 57,305 psi | 90% | 3363 fps | 99.7% |
| Unknown powder | <<locked>> | 82% | 54,868 psi | 86% | 3340 fps | 100% |
| Vihtavuori N150 | <<locked>> | 84% | 54,795 psi | 86% | 3228 fps | 100% |
| Vihtavuori N160 | <<locked>> | 82% | 55,419 psi | 87% | 3304 fps | 100% |
| Vihtavuori N165 | <<locked>> | 94% | 55,114 psi | 86% | 3307 fps | 99.3% |
| Vihtavuori N550 | <<locked>> | 82% | 56,028 psi | 88% | 3360 fps | 100% |
| Vihtavuori N555 | <<locked>> | 90% | 56,101 psi | 88% | 3376 fps | 100% |
| Vihtavuori N560 | <<locked>> | 92% | 55,854 psi | 88% | 3448 fps | 97.9% |
| Vihtavuori N565 | <<locked>> | 96% | 56,043 psi | 88% | 3419 fps | 98.2% |
| Vihtavuori N568ᴾ | <<locked>> | 100% | 56,289 psi | 88% | 3471 fps | 97.2% |
| Winchester 6.5 StaBALL | <<locked>> | 84% | 55,970 psi | 88% | 3274 fps | 100% |
| Winchester StaBALL HD | <<locked>> | 94% | 55,390 psi | 87% | 3488 fps | 100% |
| Winchester Supreme 780 | <<locked>> | 88% | 54,563 psi | 86% | 3310 fps | 98.9% |
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% | 38,551 psi | 60% | 2966 fps | 97.7% |
| Accurate 4350 | <<locked>> | 80% | 50,270 psi | 79% | 3248 fps | 100% |
| Accurate MAGPRO | <<locked>> | 90% | 51,735 psi | 81% | 3353 fps | 95.7% |
| ADI AR 2209 | <<locked>> | 80% | 41,394 psi | 65% | 3087 fps | 95.9% |
| ADI AR 2213 | <<locked>> | 86% | 45,353 psi | 71% | 3212 fps | 95.8% |
| ADI AR 2217 | <<locked>> | 94% | 44,063 psi | 69% | 3166 fps | 95.8% |
| ADI AR 2225 | <<locked>> | 90% | 35,462 psi | 56% | 2999 fps | 95.9% |
| Alliant Reloder-16 | <<locked>> | 80% | 47,079 psi | 74% | 3241 fps | 100% |
| Alliant Reloder-19 | <<locked>> | 80% | 41,510 psi | 65% | 3084 fps | 96% |
| Alliant Reloder-22 | <<locked>> | 82% | 40,321 psi | 63% | 3094 fps | 95.8% |
| Alliant Reloder-23 | <<locked>> | 80% | 36,492 psi | 57% | 2992 fps | 99.7% |
| Alliant Reloder-25 | <<locked>> | 80% | 31,966 psi | 50% | 2887 fps | 96.1% |
| Alliant Reloder-26 | <<locked>> | 80% | 40,248 psi | 63% | 3153 fps | 99.3% |
| Bofors RP15 | <<locked>> | 84% | 39,987 psi | 63% | 3084 fps | 95.5% |
| Bofors RP30 | <<locked>> | 90% | 40,669 psi | 64% | 3127 fps | 95.1% |
| Bofors RP5 | <<locked>> | 82% | 40,321 psi | 63% | 3094 fps | 95.8% |
| Bofors RP7 | <<locked>> | 80% | 51,938 psi | 81% | 3238 fps | 99.1% |
| Hodgdon H1000 | <<locked>> | 92% | 42,409 psi | 66% | 3130 fps | 95.9% |
| Hodgdon H4350 | <<locked>> | 80% | 49,066 psi | 77% | 3219 fps | 98.2% |
| Hodgdon H4831 | <<locked>> | 88% | 45,165 psi | 71% | 3146 fps | 95% |
| Hodgdon H4831 SC | <<locked>> | 86% | 47,456 psi | 74% | 3196 fps | 95.7% |
| Hodgdon Hybrid 100V | <<locked>> | 80% | 45,005 psi | 71% | 3114 fps | 100% |
| Hodgdon Retumbo | 61.5 gr | 86% | 37,608 psi | 59% | 3107 fps | 95.3% |
| Hodgdon Superformance | <<locked>> | 80% | 50,995 psi | 80% | 3314 fps | 99.2% |
| Hodgdon TrailBoss | <<locked>> | 80% | 28,181 psi | 44% | 1952 fps | 100% |
| IMR 4166 Enduron | <<locked>> | 80% | 54,172 psi | 85% | 3264 fps | 99.6% |
| IMR 4350 | <<locked>> | 80% | 47,065 psi | 74% | 3156 fps | 98.4% |
| IMR 4451 Enduron | <<locked>> | 80% | 52,649 psi | 83% | 3258 fps | 99.4% |
| IMR 4831 | <<locked>> | 80% | 43,308 psi | 68% | 3091 fps | 99.7% |
| IMR 4955 Enduron | <<locked>> | 84% | 46,441 psi | 73% | 3140 fps | 95.7% |
| IMR 7828 SSC | <<locked>> | 84% | 43,627 psi | 68% | 3182 fps | 95.3% |
| IMR 8133 Enduron | <<locked>> | 98% | 41,365 psi | 65% | 3159 fps | 95.1% |
| Lovex S065 | <<locked>> | 80% | 50,952 psi | 80% | 3212 fps | 99.8% |
| Lovex S070 | <<locked>> | 80% | 49,400 psi | 77% | 3202 fps | 99.2% |
| Lovex S071 | <<locked>> | 80% | 33,562 psi | 53% | 2835 fps | 96.1% |
| Norma 204 | <<locked>> | 80% | 47,442 psi | 74% | 3199 fps | 97.4% |
| Norma 217 | <<locked>> | 94% | 36,738 psi | 58% | 3061 fps | 95.8% |
| Norma MRP | <<locked>> | 80% | 39,566 psi | 62% | 3104 fps | 97% |
| Norma URP | <<locked>> | 80% | 48,573 psi | 76% | 3222 fps | 100% |
| Ramshot Grand | <<locked>> | 82% | 42,757 psi | 67% | 3173 fps | 95.5% |
| Ramshot Hunter | <<locked>> | 80% | 47,442 psi | 74% | 3215 fps | 99.4% |
| Ramshot Magnum | <<locked>> | 82% | 37,739 psi | 59% | 3015 fps | 95.8% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 28,921 psi | 45% | 2001 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 80% | 49,850 psi | 78% | 3261 fps | 100% |
| ReloadSwiss RS 70 | <<locked>> | 80% | 47,616 psi | 75% | 3274 fps | 99.9% |
| ReloadSwiss RS 76 | 64.3 gr | 84% | 34,809 psi | 55% | 3012 fps | 95.3% |
| ReloadSwiss RS 80 | <<locked>> | 96% | 48,153 psi | 75% | 3320 fps | 95.8% |
| Rottweil R 904 | <<locked>> | 80% | 42,670 psi | 67% | 3064 fps | 95.1% |
| Rottweil R 905 | <<locked>> | 80% | 41,118 psi | 64% | 3074 fps | 96.1% |
| Rottweil R 907 | <<locked>> | 80% | 51,938 psi | 81% | 3238 fps | 99.1% |
| Shooters World Long Rifle | <<locked>> | 80% | 50,952 psi | 80% | 3212 fps | 99.8% |
| Shooters World SW4350 | <<locked>> | 80% | 49,400 psi | 77% | 3202 fps | 99.2% |
| SNPE Vectan Tubal 7000 | <<locked>> | 80% | 49,821 psi | 78% | 3146 fps | 99.2% |
| SNPE Vectan Tubal 8000 | <<locked>> | 80% | 40,828 psi | 64% | 3068 fps | 95.9% |
| Somchem S361 | <<locked>> | 82% | 46,688 psi | 73% | 3117 fps | 95.5% |
| Somchem S365 | <<locked>> | 80% | 45,890 psi | 72% | 3176 fps | 100% |
| Somchem S385 | <<locked>> | 80% | 41,858 psi | 66% | 3054 fps | 97.1% |
| Unknown powder | <<locked>> | 80% | 51,547 psi | 81% | 3278 fps | 100% |
| Vihtavuori N150 | <<locked>> | 80% | 48,646 psi | 76% | 3123 fps | 100% |
| Vihtavuori N160 | <<locked>> | 80% | 51,851 psi | 81% | 3241 fps | 100% |
| Vihtavuori N165 | <<locked>> | 82% | 37,768 psi | 59% | 2946 fps | 95.5% |
| Vihtavuori N550 | <<locked>> | 80% | 52,765 psi | 83% | 3301 fps | 100% |
| Vihtavuori N555 | <<locked>> | 80% | 41,002 psi | 64% | 3084 fps | 99.7% |
| Vihtavuori N560 | <<locked>> | 86% | 45,803 psi | 72% | 3241 fps | 95.5% |
| Vihtavuori N565 | <<locked>> | 90% | 46,035 psi | 72% | 3219 fps | 95.9% |
| Vihtavuori N568 | <<locked>> | 96% | 49,008 psi | 77% | 3330 fps | 95.4% |
| Winchester 6.5 StaBALL | <<locked>> | 80% | 49,124 psi | 77% | 3163 fps | 100% |
| Winchester StaBALL HD | 58.8 gr | 80% | 32,996 psi | 52% | 3025 fps | 99.9% |
| Winchester Supreme 780 | <<locked>> | 80% | 41,568 psi | 65% | 3045 fps | 96.1% |
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 69 powders for .257 Weath. Mag. loaded with the .257 | 100gr | Impala RNFP KO. Hodgdon Retumbo delivers the highest muzzle velocity at 3,533 fps; across all powders the maximum-charge window runs from 2,175 fps to 3,533 fps. ADI AR 2217 gives the best case fill at 100 %, and 69 of the 69 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 100.0 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, Bofors RP30 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. Winchester StaBALL HD, ReloadSwiss RS 76, Hodgdon Retumbo rank at the top here: for .257 Weath. Mag. with the .257 | 100gr | Impala RNFP KO 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.