Load Specifications
Load data in caliber .255 GS with .257 | 100gr | Speer Varmint Hollow Point bullet and 99 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are ReloadSwiss RS 70, Alliant Reloder-17 and ReloadSwiss RS 60.
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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You can find more information in our FAQ: How can I use the Personalized Load Calculator?
Max Load - Barrel Length: 24"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| Accurate 2015 | <<locked>> | 82% | 56,724 psi | 89% | 3054 fps | 100% |
| Accurate 2495 | <<locked>> | 86% | 56,188 psi | 88% | 3081 fps | 100% |
| Accurate 2520 | <<locked>> | 82% | 57,450 psi | 90% | 3150 fps | 100% |
| Accurate 2700 | <<locked>> | 86% | 54,607 psi | 86% | 3077 fps | 97% |
| Accurate 3100ᴾ | <<locked>> | 100% | 47,384 psi | 74% | 3031 fps | 97.3% |
| Accurate 4064 | <<locked>> | 88% | 56,231 psi | 88% | 3133 fps | 100% |
| Accurate 4350 | <<locked>> | 96% | 56,826 psi | 89% | 3228 fps | 99.7% |
| ADI AR 2206H | <<locked>> | 84% | 55,796 psi | 87% | 3163 fps | 100% |
| ADI AR 2208 | <<locked>> | 90% | 56,985 psi | 89% | 3166 fps | 99.9% |
| ADI AR 2209ᴾ | <<locked>> | 100% | 54,723 psi | 86% | 3202 fps | 96.1% |
| ADI Benchmark 8208 | <<locked>> | 82% | 54,824 psi | 86% | 3110 fps | 100% |
| Alliant AR-Comp | <<locked>> | 82% | 55,927 psi | 88% | 3081 fps | 100% |
| Alliant Power Pro 2000-MR | <<locked>> | 86% | 56,144 psi | 88% | 3294 fps | 99.9% |
| Alliant Reloder- TS 15.5 | <<locked>> | 90% | 57,392 psi | 90% | 3186 fps | 100% |
| Alliant Reloder-15 | <<locked>> | 86% | 54,404 psi | 85% | 3156 fps | 99.8% |
| Alliant Reloder-16 | <<locked>> | 98% | 57,464 psi | 90% | 3287 fps | 99.9% |
| Alliant Reloder-17 | <<locked>> | 92% | 55,347 psi | 87% | 3268 fps | 100% |
| Alliant Reloder-19ᴾ | <<locked>> | 100% | 53,780 psi | 84% | 3189 fps | 96.1% |
| Alliant Reloder-23ᴾ | <<locked>> | 100% | 44,469 psi | 70% | 3058 fps | 99.6% |
| Alliant Reloder-26ᴾ | <<locked>> | 100% | 50,821 psi | 80% | 3255 fps | 99.3% |
| Baschieri & Pellagri 107 | <<locked>> | 84% | 55,796 psi | 87% | 3176 fps | 99.7% |
| Bofors RP3 | <<locked>> | 88% | 54,868 psi | 86% | 3153 fps | 100% |
| Bofors RP7 | <<locked>> | 92% | 54,534 psi | 85% | 3120 fps | 97.2% |
| Hodgdon Benchmark | <<locked>> | 82% | 56,101 psi | 88% | 3091 fps | 100% |
| Hodgdon BL-C2 | <<locked>> | 82% | 54,433 psi | 85% | 3136 fps | 100% |
| Hodgdon H380 | <<locked>> | 88% | 55,535 psi | 87% | 3166 fps | 99.4% |
| Hodgdon H414 | <<locked>> | 94% | 55,782 psi | 87% | 3222 fps | 98.1% |
| Hodgdon H4350 | <<locked>> | 92% | 55,753 psi | 87% | 3179 fps | 96.8% |
| Hodgdon H4895 | <<locked>> | 84% | 56,434 psi | 88% | 3173 fps | 100% |
| Hodgdon Hybrid 100V | <<locked>> | 98% | 54,157 psi | 85% | 3153 fps | 100% |
| Hodgdon LEVERevolution | <<locked>> | 86% | 56,391 psi | 88% | 3209 fps | 100% |
| Hodgdon Superformance | <<locked>> | 94% | 56,159 psi | 88% | 3258 fps | 97.9% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 35,911 psi | 56% | 1982 fps | 100% |
| Hodgdon VARGET | <<locked>> | 86% | 57,537 psi | 90% | 3173 fps | 100% |
| IMR 3031 | <<locked>> | 84% | 56,797 psi | 89% | 3156 fps | 100% |
| IMR 4064 | <<locked>> | 88% | 56,550 psi | 89% | 3150 fps | 99.9% |
| IMR 4166 Enduron | <<locked>> | 86% | 55,941 psi | 88% | 3120 fps | 98% |
| IMR 4350 | <<locked>> | 96% | 55,361 psi | 87% | 3150 fps | 97.4% |
| IMR 4451 Enduron | <<locked>> | 92% | 56,260 psi | 88% | 3153 fps | 98% |
| IMR 4831 | <<locked>> | 98% | 57,450 psi | 90% | 3222 fps | 99.8% |
| IMR 4895 | <<locked>> | 86% | 55,825 psi | 87% | 3189 fps | 100% |
| IMR 8208 XBR | <<locked>> | 82% | 54,824 psi | 86% | 3110 fps | 100% |
| Lovex D073.6 | <<locked>> | 84% | 56,188 psi | 88% | 3140 fps | 100% |
| Lovex S060 | <<locked>> | 84% | 54,955 psi | 86% | 3084 fps | 100% |
| Lovex S062 | <<locked>> | 88% | 56,579 psi | 89% | 3143 fps | 100% |
| Lovex S065 | <<locked>> | 94% | 56,159 psi | 88% | 3150 fps | 99% |
| Lovex S070 | <<locked>> | 96% | 57,319 psi | 90% | 3189 fps | 98.4% |
| Norma 201 | <<locked>> | 84% | 54,810 psi | 86% | 3107 fps | 100% |
| Norma 202 | <<locked>> | 84% | 55,274 psi | 87% | 3107 fps | 100% |
| Norma 203B | <<locked>> | 88% | 57,319 psi | 90% | 3199 fps | 100% |
| Norma 204 | <<locked>> | 96% | 55,985 psi | 88% | 3199 fps | 96.3% |
| Norma MRPᴾ | <<locked>> | 100% | 50,096 psi | 79% | 3199 fps | 96.9% |
| Norma URP | <<locked>> | 96% | 55,695 psi | 87% | 3212 fps | 99.6% |
| Ramshot Big Game | <<locked>> | 86% | 54,360 psi | 85% | 3166 fps | 99.9% |
| Ramshot Hunter | <<locked>> | 96% | 54,462 psi | 85% | 3205 fps | 98.6% |
| Ramshot TAC | <<locked>> | 82% | 54,926 psi | 86% | 3127 fps | 99% |
| Ramshot Wild Boar | <<locked>> | 82% | 54,911 psi | 86% | 3146 fps | 99.9% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 36,332 psi | 57% | 2024 fps | 100% |
| ReloadSwiss RS 50 | <<locked>> | 88% | 55,709 psi | 87% | 3143 fps | 98.4% |
| ReloadSwiss RS 52 | <<locked>> | 84% | 55,085 psi | 86% | 3228 fps | 99.8% |
| ReloadSwiss RS 60 | <<locked>> | 90% | 54,998 psi | 86% | 3264 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 96% | 56,840 psi | 89% | 3251 fps | 99.7% |
| ReloadSwiss RS 70 | <<locked>> | 96% | 55,796 psi | 87% | 3281 fps | 99.5% |
| Rottweil R 901 | <<locked>> | 82% | 55,550 psi | 87% | 3087 fps | 100% |
| Rottweil R 902 | <<locked>> | 86% | 55,405 psi | 87% | 3107 fps | 100% |
| Rottweil R 903 | <<locked>> | 90% | 54,708 psi | 86% | 3143 fps | 100% |
| Rottweil R 905ᴾ | <<locked>> | 100% | 52,794 psi | 83% | 3169 fps | 96.1% |
| Rottweil R 907 | <<locked>> | 92% | 54,534 psi | 85% | 3120 fps | 97.2% |
| Shooters World Long Rifle | <<locked>> | 94% | 56,159 psi | 88% | 3150 fps | 99% |
| Shooters World Match Rifle | <<locked>> | 84% | 56,188 psi | 88% | 3140 fps | 100% |
| Shooters World Precision | <<locked>> | 88% | 56,579 psi | 89% | 3143 fps | 100% |
| Shooters World SW4350 | <<locked>> | 96% | 57,319 psi | 90% | 3189 fps | 98.4% |
| SNPE Vectan SP 11 | <<locked>> | 90% | 56,478 psi | 89% | 3209 fps | 100% |
| SNPE Vectan SP 3 | <<locked>> | 84% | 56,115 psi | 88% | 3022 fps | 100% |
| SNPE Vectan SP 7 | <<locked>> | 84% | 57,377 psi | 90% | 3163 fps | 99.5% |
| SNPE Vectan SP 9 | <<locked>> | 84% | 54,433 psi | 85% | 3130 fps | 99.9% |
| SNPE Vectan Tubal 3000 | <<locked>> | 84% | 55,738 psi | 87% | 3041 fps | 100% |
| SNPE Vectan Tubal 5000 | <<locked>> | 90% | 56,333 psi | 88% | 3035 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 94% | 56,289 psi | 88% | 3097 fps | 98% |
| SNPE Vectan Tubal 8000ᴾ | <<locked>> | 100% | 52,301 psi | 82% | 3163 fps | 95.9% |
| Somchem S335 | <<locked>> | 84% | 55,492 psi | 87% | 3038 fps | 100% |
| Somchem S341 | <<locked>> | 84% | 56,855 psi | 89% | 3150 fps | 100% |
| Somchem S355 | <<locked>> | 90% | 54,897 psi | 86% | 3143 fps | 100% |
| Somchem S365 | <<locked>> | 98% | 54,157 psi | 85% | 3215 fps | 100% |
| Somchem S385ᴾ | <<locked>> | 100% | 53,287 psi | 84% | 3143 fps | 97% |
| Vihtavuori N133 | <<locked>> | 84% | 56,115 psi | 88% | 3022 fps | 100% |
| Vihtavuori N135 | <<locked>> | 86% | 55,230 psi | 87% | 3068 fps | 100% |
| Vihtavuori N140 | <<locked>> | 86% | 55,869 psi | 88% | 3081 fps | 100% |
| Vihtavuori N150 | <<locked>> | 92% | 56,449 psi | 88% | 3120 fps | 100% |
| Vihtavuori N160 | <<locked>> | 94% | 54,462 psi | 85% | 3153 fps | 99.5% |
| Vihtavuori N530 | <<locked>> | 82% | 55,013 psi | 86% | 3107 fps | 100% |
| Vihtavuori N540 | <<locked>> | 88% | 57,696 psi | 90% | 3130 fps | 100% |
| Vihtavuori N550 | <<locked>> | 96% | 56,971 psi | 89% | 3212 fps | 99.6% |
| Vihtavuori N555ᴾ | <<locked>> | 100% | 49,545 psi | 78% | 3143 fps | 99.5% |
| Winchester 6.5 StaBALL | <<locked>> | 94% | 54,447 psi | 85% | 3123 fps | 100% |
| Winchester 748 | <<locked>> | 82% | 55,535 psi | 87% | 3159 fps | 100% |
| Winchester 760 | <<locked>> | 94% | 55,782 psi | 87% | 3222 fps | 98.1% |
| Winchester StaBALL HDᴾ | <<locked>> | 100% | 40,103 psi | 63% | 3081 fps | 99.7% |
| Winchester StaBALL Match | <<locked>> | 84% | 54,534 psi | 85% | 3140 fps | 100% |
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 2015 | <<locked>> | 80% | 53,055 psi | 83% | 3002 fps | 100% |
| Accurate 2495 | <<locked>> | 80% | 46,253 psi | 72% | 2927 fps | 100% |
| Accurate 2520 | <<locked>> | 80% | 53,693 psi | 84% | 3091 fps | 100% |
| Accurate 2700 | <<locked>> | 82% | 47,935 psi | 75% | 2956 fps | 95.5% |
| Accurate 3100 | <<locked>> | 96% | 41,046 psi | 64% | 2904 fps | 95.6% |
| Accurate 4064 | <<locked>> | 80% | 43,758 psi | 69% | 2920 fps | 100% |
| Accurate 4350 | <<locked>> | 82% | 35,012 psi | 55% | 2785 fps | 95.4% |
| ADI AR 2206H | <<locked>> | 80% | 49,255 psi | 77% | 3048 fps | 99.6% |
| ADI AR 2208 | <<locked>> | 80% | 41,698 psi | 65% | 2877 fps | 98% |
| ADI AR 2209 | <<locked>> | 98% | 51,126 psi | 80% | 3133 fps | 95.2% |
| ADI Benchmark 8208 | <<locked>> | 80% | 51,358 psi | 80% | 3054 fps | 100% |
| Alliant AR-Comp | <<locked>> | 80% | 52,431 psi | 82% | 3031 fps | 100% |
| Alliant Power Pro 2000-MR | <<locked>> | 80% | 45,455 psi | 71% | 3091 fps | 98.8% |
| Alliant Reloder- TS 15.5 | <<locked>> | 80% | 41,858 psi | 66% | 2907 fps | 99.2% |
| Alliant Reloder-15 | <<locked>> | 80% | 44,875 psi | 70% | 2976 fps | 98.8% |
| Alliant Reloder-16 | <<locked>> | 82% | 34,577 psi | 54% | 2795 fps | 95.3% |
| Alliant Reloder-17 | 44.8 gr | 80% | 36,463 psi | 57% | 2874 fps | 97.9% |
| Alliant Reloder-19 | <<locked>> | 98% | 50,314 psi | 79% | 3123 fps | 95.2% |
| Alliant Reloder-23 | <<locked>> | 88% | 30,284 psi | 47% | 2690 fps | 95.1% |
| Alliant Reloder-26 | <<locked>> | 92% | 37,927 psi | 59% | 2963 fps | 96% |
| Baschieri & Pellagri 107 | <<locked>> | 80% | 48,733 psi | 76% | 3051 fps | 99% |
| Bofors RP3 | <<locked>> | 80% | 41,959 psi | 66% | 2913 fps | 99.3% |
| Bofors RP7 | <<locked>> | 88% | 48,080 psi | 75% | 2999 fps | 95.8% |
| Hodgdon Benchmark | <<locked>> | 80% | 52,620 psi | 82% | 3035 fps | 100% |
| Hodgdon BL-C2 | <<locked>> | 80% | 50,923 psi | 80% | 3077 fps | 100% |
| Hodgdon H380 | <<locked>> | 80% | 42,409 psi | 66% | 2913 fps | 97.2% |
| Hodgdon H414 | <<locked>> | 88% | 45,556 psi | 71% | 3028 fps | 95.8% |
| Hodgdon H4350 | <<locked>> | 88% | 49,168 psi | 77% | 3058 fps | 95.3% |
| Hodgdon H4895 | <<locked>> | 80% | 49,763 psi | 78% | 3061 fps | 99.8% |
| Hodgdon Hybrid 100V | <<locked>> | 80% | 29,950 psi | 47% | 2625 fps | 95.2% |
| Hodgdon LEVERevolution | <<locked>> | 80% | 46,108 psi | 72% | 3028 fps | 99.7% |
| Hodgdon Superformance | <<locked>> | 88% | 45,281 psi | 71% | 3048 fps | 95.2% |
| Hodgdon TrailBoss | <<locked>> | 80% | 26,760 psi | 42% | 1775 fps | 100% |
| Hodgdon VARGET | <<locked>> | 80% | 47,761 psi | 75% | 3005 fps | 99.7% |
| IMR 3031 | <<locked>> | 80% | 50,009 psi | 78% | 3051 fps | 100% |
| IMR 4064 | <<locked>> | 80% | 43,816 psi | 69% | 2917 fps | 98.6% |
| IMR 4166 Enduron | <<locked>> | 80% | 46,325 psi | 73% | 2943 fps | 96% |
| IMR 4350 | <<locked>> | 90% | 45,730 psi | 72% | 2969 fps | 95.2% |
| IMR 4451 Enduron | <<locked>> | 84% | 43,961 psi | 69% | 2917 fps | 95.2% |
| IMR 4831 | <<locked>> | 82% | 33,794 psi | 53% | 2740 fps | 95% |
| IMR 4895 | <<locked>> | 80% | 45,992 psi | 72% | 3009 fps | 99.3% |
| IMR 8208 XBR | <<locked>> | 80% | 51,358 psi | 80% | 3054 fps | 100% |
| Lovex D073.6 | <<locked>> | 80% | 49,037 psi | 77% | 3022 fps | 100% |
| Lovex S060 | <<locked>> | 80% | 48,602 psi | 76% | 2972 fps | 99.6% |
| Lovex S062 | <<locked>> | 80% | 43,947 psi | 69% | 2920 fps | 99.7% |
| Lovex S065 | <<locked>> | 82% | 38,609 psi | 61% | 2799 fps | 95.1% |
| Lovex S070 | <<locked>> | 88% | 44,614 psi | 70% | 2953 fps | 95.8% |
| Norma 201 | <<locked>> | 80% | 48,298 psi | 76% | 2995 fps | 99.9% |
| Norma 202 | <<locked>> | 80% | 48,689 psi | 76% | 2999 fps | 100% |
| Norma 203B | <<locked>> | 80% | 44,222 psi | 69% | 2963 fps | 99% |
| Norma 204 | <<locked>> | 94% | 52,272 psi | 82% | 3136 fps | 95.5% |
| Norma MRP | <<locked>> | 96% | 43,656 psi | 68% | 3061 fps | 95% |
| Norma URP | <<locked>> | 82% | 35,027 psi | 55% | 2785 fps | 95.2% |
| Ramshot Big Game | <<locked>> | 80% | 44,251 psi | 69% | 2979 fps | 98.9% |
| Ramshot Hunter | <<locked>> | 88% | 41,640 psi | 65% | 2953 fps | 95.6% |
| Ramshot TAC | <<locked>> | 80% | 51,271 psi | 80% | 3061 fps | 98.4% |
| Ramshot Wild Boar | <<locked>> | 80% | 51,184 psi | 80% | 3081 fps | 99.7% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 27,209 psi | 43% | 1818 fps | 100% |
| ReloadSwiss RS 50 | <<locked>> | 80% | 42,699 psi | 67% | 2894 fps | 95.6% |
| ReloadSwiss RS 52 | <<locked>> | 80% | 47,964 psi | 75% | 3097 fps | 99.2% |
| ReloadSwiss RS 60 | 44.8 gr | 80% | 38,798 psi | 61% | 2949 fps | 99.9% |
| ReloadSwiss RS 62 | <<locked>> | 84% | 37,260 psi | 58% | 2864 fps | 95.8% |
| ReloadSwiss RS 70 | 48.9 gr | 86% | 39,363 psi | 62% | 2936 fps | 95.9% |
| Rottweil R 901 | <<locked>> | 80% | 52,344 psi | 82% | 3038 fps | 100% |
| Rottweil R 902 | <<locked>> | 80% | 45,977 psi | 72% | 2940 fps | 99.8% |
| Rottweil R 903 | <<locked>> | 80% | 39,305 psi | 62% | 2848 fps | 98.6% |
| Rottweil R 905 | <<locked>> | 98% | 49,182 psi | 77% | 3100 fps | 95.1% |
| Rottweil R 907 | <<locked>> | 88% | 48,080 psi | 75% | 2999 fps | 95.8% |
| Shooters World Long Rifle | <<locked>> | 82% | 38,609 psi | 61% | 2799 fps | 95.1% |
| Shooters World Match Rifle | <<locked>> | 80% | 49,037 psi | 77% | 3022 fps | 100% |
| Shooters World Precision | <<locked>> | 80% | 43,947 psi | 69% | 2920 fps | 99.7% |
| Shooters World SW4350 | <<locked>> | 88% | 44,614 psi | 70% | 2953 fps | 95.8% |
| SNPE Vectan SP 11 | <<locked>> | 80% | 40,437 psi | 63% | 2904 fps | 98.2% |
| SNPE Vectan SP 3 | <<locked>> | 80% | 49,719 psi | 78% | 2927 fps | 100% |
| SNPE Vectan SP 7 | <<locked>> | 80% | 49,980 psi | 78% | 3038 fps | 98.6% |
| SNPE Vectan SP 9 | <<locked>> | 80% | 47,776 psi | 75% | 3012 fps | 99.5% |
| SNPE Vectan Tubal 3000 | <<locked>> | 80% | 49,269 psi | 77% | 2936 fps | 100% |
| SNPE Vectan Tubal 5000 | <<locked>> | 80% | 41,350 psi | 65% | 2789 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 86% | 43,265 psi | 68% | 2858 fps | 95.2% |
| SNPE Vectan Tubal 8000 | <<locked>> | 98% | 48,704 psi | 76% | 3097 fps | 95% |
| Somchem S335 | <<locked>> | 80% | 49,052 psi | 77% | 2936 fps | 100% |
| Somchem S341 | <<locked>> | 80% | 49,588 psi | 78% | 3028 fps | 99.6% |
| Somchem S355 | <<locked>> | 80% | 40,074 psi | 63% | 2854 fps | 98.6% |
| Somchem S365 | <<locked>> | 80% | 29,457 psi | 46% | 2671 fps | 96.6% |
| Somchem S385 | <<locked>> | 96% | 46,804 psi | 73% | 3022 fps | 95.5% |
| Vihtavuori N133 | <<locked>> | 80% | 49,719 psi | 78% | 2927 fps | 100% |
| Vihtavuori N135 | <<locked>> | 80% | 45,788 psi | 72% | 2917 fps | 100% |
| Vihtavuori N140 | <<locked>> | 80% | 46,050 psi | 72% | 2923 fps | 100% |
| Vihtavuori N150 | <<locked>> | 80% | 38,029 psi | 60% | 2782 fps | 99.2% |
| Vihtavuori N160 | <<locked>> | 82% | 36,550 psi | 57% | 2789 fps | 95.8% |
| Vihtavuori N530 | <<locked>> | 80% | 51,750 psi | 81% | 3051 fps | 100% |
| Vihtavuori N540 | <<locked>> | 80% | 44,512 psi | 70% | 2910 fps | 100% |
| Vihtavuori N550 | <<locked>> | 82% | 35,955 psi | 56% | 2785 fps | 95.3% |
| Vihtavuori N555 | <<locked>> | 88% | 33,054 psi | 52% | 2776 fps | 95.3% |
| Winchester 6.5 StaBALL | <<locked>> | 80% | 33,634 psi | 53% | 2697 fps | 97.1% |
| Winchester 748 | <<locked>> | 80% | 51,924 psi | 81% | 3100 fps | 100% |
| Winchester 760 | <<locked>> | 88% | 45,556 psi | 71% | 3028 fps | 95.8% |
| Winchester StaBALL HD | <<locked>> | 92% | 30,690 psi | 48% | 2785 fps | 96.1% |
| Winchester StaBALL Match | <<locked>> | 80% | 47,514 psi | 74% | 3015 fps | 99.7% |
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 99 powders for .255 GS loaded with the .257 | 100gr | Speer Varmint Hollow Point. Alliant Power Pro 2000-MR delivers the highest muzzle velocity at 3,294 fps; across all powders the maximum-charge window runs from 1,982 fps to 3,294 fps. Accurate 3100 gives the best case fill at 100 %, and 99 of the 99 powders fall inside the usable 80–100 % fill window.
Relative to the caliber's maximum pressure (440 MPa), the top charges use 56–90 %, leaving at least 10 % headroom. The 100.0 gr projectile in 0.257" calls for a 1:12.0 twist; slower twists will usually not stabilise this weight. Accurate 3100, ADI AR 2209, Alliant Reloder-19 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. ReloadSwiss RS 70, Alliant Reloder-17, ReloadSwiss RS 60 rank at the top here: for .255 GS with the .257 | 100gr | Speer Varmint Hollow Point 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.