Load Specifications
Load data in caliber .257 Weath. Mag. with .257 | 100gr | Speer Boat-Tail bullet and 75 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are IMR 7828 SSC, Winchester StaBALL HD 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 2700 | <<locked>> | 82% | 57,174 psi | 90% | 3297 fps | 99.6% |
| Accurate 3100 | <<locked>> | 94% | 57,421 psi | 90% | 3360 fps | 100% |
| Accurate 4350 | <<locked>> | 84% | 54,375 psi | 85% | 3340 fps | 100% |
| Accurate MAGPRO | <<locked>> | 94% | 57,043 psi | 89% | 3468 fps | 97.1% |
| ADI AR 2209 | <<locked>> | 90% | 55,317 psi | 87% | 3399 fps | 99.1% |
| ADI AR 2213 | <<locked>> | 94% | 57,043 psi | 89% | 3465 fps | 98.6% |
| ADI AR 2217ᴾ | <<locked>> | 100% | 51,547 psi | 81% | 3346 fps | 98% |
| ADI AR 2225ᴾ | <<locked>> | 100% | 46,209 psi | 72% | 3297 fps | 99.4% |
| Alliant Reloder-16 | <<locked>> | 86% | 55,230 psi | 87% | 3406 fps | 100% |
| Alliant Reloder-17 | <<locked>> | 82% | 56,550 psi | 89% | 3419 fps | 100% |
| Alliant Reloder-19 | <<locked>> | 90% | 54,998 psi | 86% | 3386 fps | 99.1% |
| Alliant Reloder-22 | <<locked>> | 94% | 57,188 psi | 90% | 3461 fps | 99.4% |
| Alliant Reloder-23 | <<locked>> | 94% | 54,795 psi | 86% | 3373 fps | 100% |
| Alliant Reloder-25 | <<locked>> | 98% | 54,302 psi | 85% | 3432 fps | 100% |
| Alliant Reloder-26 | <<locked>> | 90% | 55,361 psi | 87% | 3465 fps | 100% |
| Bofors RP15 | <<locked>> | 96% | 56,347 psi | 88% | 3442 fps | 99.2% |
| Bofors RP30ᴾ | <<locked>> | 100% | 54,302 psi | 85% | 3428 fps | 98.6% |
| Bofors RP5 | <<locked>> | 94% | 57,188 psi | 90% | 3461 fps | 99.4% |
| Bofors RP7 | <<locked>> | 84% | 56,550 psi | 89% | 3343 fps | 99.6% |
| Hodgdon H1000ᴾ | <<locked>> | 100% | 52,953 psi | 83% | 3379 fps | 98.7% |
| Hodgdon H414 | <<locked>> | 82% | 57,058 psi | 89% | 3415 fps | 99.9% |
| Hodgdon H4350 | <<locked>> | 86% | 57,058 psi | 89% | 3389 fps | 99.4% |
| Hodgdon H4831 | <<locked>> | 96% | 56,391 psi | 88% | 3386 fps | 97.9% |
| Hodgdon H4831 SC | <<locked>> | 92% | 55,869 psi | 88% | 3376 fps | 97.8% |
| Hodgdon Hybrid 100V | <<locked>> | 88% | 55,564 psi | 87% | 3317 fps | 100% |
| Hodgdon Retumboᴾ | <<locked>> | 100% | 57,174 psi | 90% | 3579 fps | 99.9% |
| Hodgdon Superformance | <<locked>> | 84% | 57,014 psi | 89% | 3438 fps | 99.8% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 37,028 psi | 58% | 2182 fps | 100% |
| IMR 4064 | <<locked>> | 82% | 57,580 psi | 90% | 3333 fps | 100% |
| IMR 4166 Enduron | <<locked>> | 82% | 55,738 psi | 87% | 3310 fps | 99.8% |
| IMR 4350 | <<locked>> | 86% | 54,694 psi | 86% | 3320 fps | 99.5% |
| IMR 4451 Enduron | <<locked>> | 82% | 54,520 psi | 85% | 3307 fps | 99.7% |
| IMR 4831 | <<locked>> | 90% | 56,188 psi | 88% | 3353 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 90% | 54,085 psi | 85% | 3310 fps | 97.6% |
| IMR 7828 SSC | <<locked>> | 92% | 55,274 psi | 87% | 3445 fps | 98.4% |
| Lovex S065 | <<locked>> | 84% | 55,172 psi | 86% | 3307 fps | 100% |
| Lovex S070 | <<locked>> | 86% | 56,971 psi | 89% | 3360 fps | 99.9% |
| Lovex S071 | <<locked>> | 98% | 54,795 psi | 86% | 3317 fps | 100% |
| Norma 204 | <<locked>> | 86% | 55,811 psi | 87% | 3379 fps | 99% |
| Norma 217ᴾ | <<locked>> | 100% | 41,858 psi | 66% | 3209 fps | 97.8% |
| Norma MRP | <<locked>> | 92% | 57,435 psi | 90% | 3491 fps | 99.9% |
| Norma URP | <<locked>> | 86% | 56,492 psi | 89% | 3379 fps | 100% |
| Ramshot Grand | <<locked>> | 90% | 55,100 psi | 86% | 3448 fps | 98.7% |
| Ramshot Hunter | <<locked>> | 86% | 55,448 psi | 87% | 3383 fps | 100% |
| Ramshot Magnum | <<locked>> | 94% | 56,637 psi | 89% | 3422 fps | 99.8% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 37,913 psi | 59% | 2234 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 84% | 54,737 psi | 86% | 3363 fps | 100% |
| ReloadSwiss RS 70 | <<locked>> | 86% | 57,029 psi | 89% | 3458 fps | 100% |
| ReloadSwiss RS 76 | <<locked>> | 98% | 54,157 psi | 85% | 3497 fps | 100% |
| ReloadSwiss RS 80ᴾ | <<locked>> | 100% | 53,316 psi | 84% | 3438 fps | 97.3% |
| Rottweil R 904 | <<locked>> | 90% | 56,550 psi | 89% | 3366 fps | 98.5% |
| Rottweil R 905 | <<locked>> | 90% | 54,505 psi | 85% | 3373 fps | 99.1% |
| Rottweil R 907 | <<locked>> | 84% | 56,550 psi | 89% | 3343 fps | 99.6% |
| Shooters World Long Rifle | <<locked>> | 84% | 55,172 psi | 86% | 3307 fps | 100% |
| Shooters World SW4350 | <<locked>> | 86% | 56,971 psi | 89% | 3360 fps | 99.9% |
| SNPE Vectan Tubal 5000 | <<locked>> | 82% | 57,319 psi | 90% | 3199 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 84% | 54,520 psi | 85% | 3255 fps | 99.7% |
| SNPE Vectan Tubal 8000 | <<locked>> | 92% | 57,725 psi | 90% | 3432 fps | 99.4% |
| Somchem S355 | <<locked>> | 82% | 57,580 psi | 90% | 3340 fps | 100% |
| Somchem S361 | <<locked>> | 88% | 54,491 psi | 85% | 3284 fps | 97.5% |
| Somchem S365 | <<locked>> | 88% | 57,276 psi | 90% | 3383 fps | 100% |
| Somchem S385 | <<locked>> | 90% | 55,056 psi | 86% | 3343 fps | 99.5% |
| Unknown powder | <<locked>> | 84% | 56,521 psi | 89% | 3383 fps | 100% |
| Vihtavuori N150 | <<locked>> | 86% | 55,898 psi | 88% | 3261 fps | 100% |
| Vihtavuori N160 | <<locked>> | 84% | 56,985 psi | 89% | 3346 fps | 100% |
| Vihtavuori N165 | <<locked>> | 96% | 56,507 psi | 89% | 3346 fps | 99.5% |
| Vihtavuori N550 | <<locked>> | 84% | 57,696 psi | 90% | 3402 fps | 100% |
| Vihtavuori N555 | <<locked>> | 92% | 56,855 psi | 89% | 3402 fps | 100% |
| Vihtavuori N560 | <<locked>> | 94% | 57,667 psi | 90% | 3494 fps | 98.3% |
| Vihtavuori N565 | <<locked>> | 98% | 57,348 psi | 90% | 3455 fps | 98.5% |
| Vihtavuori N568ᴾ | <<locked>> | 100% | 54,085 psi | 85% | 3442 fps | 96.8% |
| Winchester 6.5 StaBALL | <<locked>> | 84% | 54,259 psi | 85% | 3258 fps | 100% |
| Winchester 760 | <<locked>> | 82% | 57,058 psi | 89% | 3415 fps | 99.9% |
| Winchester StaBALL HD | <<locked>> | 96% | 57,058 psi | 89% | 3520 fps | 100% |
| Winchester Supreme 780 | <<locked>> | 90% | 56,652 psi | 89% | 3360 fps | 99.2% |
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 2700 | <<locked>> | 80% | 53,287 psi | 84% | 3228 fps | 99.3% |
| Accurate 3100 | <<locked>> | 80% | 35,433 psi | 56% | 2907 fps | 96.8% |
| Accurate 4350 | <<locked>> | 80% | 47,384 psi | 74% | 3212 fps | 100% |
| Accurate MAGPRO | <<locked>> | 90% | 49,371 psi | 77% | 3317 fps | 95.2% |
| ADI AR 2209 | <<locked>> | 80% | 39,421 psi | 62% | 3054 fps | 95.3% |
| ADI AR 2213 | <<locked>> | 86% | 43,395 psi | 68% | 3182 fps | 95.3% |
| ADI AR 2217 | <<locked>> | 94% | 41,989 psi | 66% | 3133 fps | 95.2% |
| ADI AR 2225 | <<locked>> | 92% | 35,288 psi | 55% | 3009 fps | 95.9% |
| Alliant Reloder-16 | <<locked>> | 80% | 45,223 psi | 71% | 3219 fps | 100% |
| Alliant Reloder-17 | <<locked>> | 80% | 52,692 psi | 83% | 3356 fps | 100% |
| Alliant Reloder-19 | <<locked>> | 80% | 39,465 psi | 62% | 3051 fps | 95.4% |
| Alliant Reloder-22 | <<locked>> | 84% | 40,669 psi | 64% | 3117 fps | 96% |
| Alliant Reloder-23 | <<locked>> | 80% | 34,069 psi | 53% | 2943 fps | 99.3% |
| Alliant Reloder-25 | <<locked>> | 82% | 31,575 psi | 49% | 2890 fps | 95.9% |
| Alliant Reloder-26 | <<locked>> | 80% | 37,594 psi | 59% | 3097 fps | 98.8% |
| Bofors RP15 | <<locked>> | 86% | 40,350 psi | 63% | 3107 fps | 95.7% |
| Bofors RP30 | <<locked>> | 92% | 40,886 psi | 64% | 3143 fps | 95.2% |
| Bofors RP5 | <<locked>> | 84% | 40,669 psi | 64% | 3117 fps | 96% |
| Bofors RP7 | <<locked>> | 80% | 49,676 psi | 78% | 3212 fps | 98.9% |
| Hodgdon H1000 | <<locked>> | 92% | 40,176 psi | 63% | 3091 fps | 95.2% |
| Hodgdon H414 | <<locked>> | 80% | 53,330 psi | 84% | 3350 fps | 99.6% |
| Hodgdon H4350 | <<locked>> | 80% | 47,297 psi | 74% | 3199 fps | 97.9% |
| Hodgdon H4831 | <<locked>> | 90% | 46,151 psi | 72% | 3182 fps | 95.5% |
| Hodgdon H4831 SC | <<locked>> | 86% | 45,498 psi | 71% | 3169 fps | 95.3% |
| Hodgdon Hybrid 100V | <<locked>> | 80% | 42,656 psi | 67% | 3081 fps | 100% |
| Hodgdon Retumbo | 64.4 gr | 88% | 37,826 psi | 59% | 3130 fps | 95.5% |
| Hodgdon Superformance | <<locked>> | 80% | 48,863 psi | 77% | 3287 fps | 99% |
| Hodgdon TrailBoss | <<locked>> | 80% | 27,717 psi | 43% | 1959 fps | 100% |
| IMR 4064 | <<locked>> | 80% | 54,085 psi | 85% | 3274 fps | 100% |
| IMR 4166 Enduron | <<locked>> | 80% | 52,431 psi | 82% | 3251 fps | 99.5% |
| IMR 4350 | <<locked>> | 80% | 45,194 psi | 71% | 3133 fps | 98.1% |
| IMR 4451 Enduron | <<locked>> | 80% | 51,039 psi | 80% | 3245 fps | 99.3% |
| IMR 4831 | <<locked>> | 80% | 40,712 psi | 64% | 3051 fps | 99.4% |
| IMR 4955 Enduron | <<locked>> | 84% | 44,730 psi | 70% | 3120 fps | 95.3% |
| IMR 7828 SSC | 64.3 gr | 86% | 44,614 psi | 70% | 3222 fps | 95.8% |
| Lovex S065 | <<locked>> | 80% | 48,791 psi | 76% | 3189 fps | 99.7% |
| Lovex S070 | <<locked>> | 80% | 47,108 psi | 74% | 3173 fps | 99% |
| Lovex S071 | <<locked>> | 82% | 32,503 psi | 51% | 2825 fps | 95.7% |
| Norma 204 | <<locked>> | 80% | 45,368 psi | 71% | 3173 fps | 97% |
| Norma 217 | <<locked>> | 96% | 36,376 psi | 57% | 3064 fps | 95.8% |
| Norma MRP | <<locked>> | 80% | 37,014 psi | 58% | 3051 fps | 96.1% |
| Norma URP | <<locked>> | 80% | 46,354 psi | 73% | 3196 fps | 99.9% |
| Ramshot Grand | <<locked>> | 84% | 43,700 psi | 68% | 3212 fps | 96% |
| Ramshot Hunter | <<locked>> | 80% | 45,252 psi | 71% | 3186 fps | 99.1% |
| Ramshot Magnum | <<locked>> | 84% | 38,232 psi | 60% | 3041 fps | 96.1% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 28,369 psi | 44% | 2005 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 80% | 47,442 psi | 74% | 3232 fps | 99.9% |
| ReloadSwiss RS 70 | <<locked>> | 80% | 45,629 psi | 72% | 3248 fps | 99.8% |
| ReloadSwiss RS 76 | <<locked>> | 86% | 34,650 psi | 54% | 3022 fps | 95.4% |
| ReloadSwiss RS 80 | <<locked>> | 96% | 45,672 psi | 72% | 3281 fps | 95.2% |
| Rottweil R 904 | <<locked>> | 82% | 43,453 psi | 68% | 3100 fps | 95.5% |
| Rottweil R 905 | <<locked>> | 80% | 38,856 psi | 61% | 3035 fps | 95.4% |
| Rottweil R 907 | <<locked>> | 80% | 49,676 psi | 78% | 3212 fps | 98.9% |
| Shooters World Long Rifle | <<locked>> | 80% | 48,791 psi | 76% | 3189 fps | 99.7% |
| Shooters World SW4350 | <<locked>> | 80% | 47,108 psi | 74% | 3173 fps | 99% |
| SNPE Vectan Tubal 5000 | <<locked>> | 80% | 54,070 psi | 85% | 3150 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 80% | 47,630 psi | 75% | 3123 fps | 99% |
| SNPE Vectan Tubal 8000 | <<locked>> | 80% | 38,522 psi | 60% | 3028 fps | 95.2% |
| Somchem S355 | <<locked>> | 80% | 54,114 psi | 85% | 3281 fps | 100% |
| Somchem S361 | <<locked>> | 82% | 44,628 psi | 70% | 3087 fps | 95.1% |
| Somchem S365 | <<locked>> | 80% | 43,439 psi | 68% | 3143 fps | 100% |
| Somchem S385 | <<locked>> | 80% | 39,334 psi | 62% | 3012 fps | 96.5% |
| Unknown powder | <<locked>> | 80% | 49,516 psi | 78% | 3258 fps | 99.9% |
| Vihtavuori N150 | <<locked>> | 80% | 46,369 psi | 73% | 3100 fps | 100% |
| Vihtavuori N160 | <<locked>> | 80% | 49,719 psi | 78% | 3222 fps | 100% |
| Vihtavuori N165 | <<locked>> | 84% | 38,000 psi | 60% | 2969 fps | 95.7% |
| Vihtavuori N550 | <<locked>> | 80% | 50,459 psi | 79% | 3274 fps | 100% |
| Vihtavuori N555 | <<locked>> | 80% | 38,203 psi | 60% | 3031 fps | 99.3% |
| Vihtavuori N560 | <<locked>> | 88% | 46,775 psi | 73% | 3278 fps | 95.9% |
| Vihtavuori N565 | <<locked>> | 90% | 43,381 psi | 68% | 3173 fps | 95.1% |
| Vihtavuori N568 | <<locked>> | 98% | 50,343 psi | 79% | 3366 fps | 95.9% |
| Winchester 6.5 StaBALL | <<locked>> | 80% | 47,007 psi | 74% | 3136 fps | 100% |
| Winchester 760 | <<locked>> | 80% | 53,330 psi | 84% | 3350 fps | 99.6% |
| Winchester StaBALL HD | 60.1 gr | 80% | 30,313 psi | 48% | 2949 fps | 99.4% |
| Winchester Supreme 780 | <<locked>> | 80% | 39,378 psi | 62% | 3009 fps | 95.4% |
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 80 powders for .257 Weath. Mag. loaded with the .257 | 100gr | Speer Boat-Tail. Hodgdon Retumbo delivers the highest muzzle velocity at 3,579 fps; across all powders the maximum-charge window runs from 2,182 fps to 3,579 fps. ADI AR 2217 gives the best case fill at 100 %, and 80 of the 80 powders fall inside the usable 80–100 % fill window.
Relative to the caliber's maximum pressure (440 MPa), the top charges use 58–90 %, leaving at least 10 % headroom. The 100.0 gr projectile in 0.257" calls for a 1:11.5 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. IMR 7828 SSC, Winchester StaBALL HD, Hodgdon Retumbo rank at the top here: for .257 Weath. Mag. with the .257 | 100gr | Speer Boat-Tail they combine a high case fill with complete burn and sit in the upper velocity band. As outliers, Alliant Reloder-33, IMR 7977 Enduron, Vihtavuori N570 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.