Load Specifications
Load data in caliber .255 GS with .257 | 100gr | Osprey Virtus bullet and 97 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are ReloadSwiss RS 70, Hodgdon Superformance and Alliant Reloder-17.
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.
A valid access license is required to use the Personalized Load Calculator.
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>> | 84% | 57,072 psi | 89% | 3058 fps | 100% |
| Accurate 2495 | <<locked>> | 88% | 56,043 psi | 88% | 3081 fps | 100% |
| Accurate 2520 | <<locked>> | 82% | 54,360 psi | 85% | 3100 fps | 100% |
| Accurate 2700 | <<locked>> | 88% | 55,521 psi | 87% | 3087 fps | 97% |
| Accurate 3100ᴾ | <<locked>> | 100% | 43,671 psi | 68% | 2959 fps | 96.2% |
| Accurate 4064 | <<locked>> | 90% | 56,188 psi | 88% | 3130 fps | 100% |
| Accurate 4350 | <<locked>> | 98% | 57,203 psi | 90% | 3232 fps | 99.7% |
| ADI AR 2206H | <<locked>> | 86% | 56,797 psi | 89% | 3173 fps | 100% |
| ADI AR 2208 | <<locked>> | 90% | 54,520 psi | 85% | 3120 fps | 99.7% |
| ADI Benchmark 8208 | <<locked>> | 84% | 55,448 psi | 87% | 3117 fps | 100% |
| Alliant AR-Comp | <<locked>> | 84% | 56,637 psi | 89% | 3091 fps | 100% |
| Alliant Power Pro 2000-MR | <<locked>> | 88% | 57,101 psi | 89% | 3307 fps | 99.9% |
| Alliant Reloder- TS 15.5 | <<locked>> | 90% | 54,592 psi | 86% | 3143 fps | 100% |
| Alliant Reloder-15 | <<locked>> | 88% | 54,940 psi | 86% | 3163 fps | 99.8% |
| Alliant Reloder-16 | <<locked>> | 98% | 54,317 psi | 85% | 3232 fps | 99.7% |
| Alliant Reloder-17 | <<locked>> | 94% | 55,956 psi | 88% | 3274 fps | 100% |
| Alliant Reloder-23ᴾ | <<locked>> | 100% | 41,597 psi | 65% | 2995 fps | 99% |
| Alliant Reloder-26ᴾ | <<locked>> | 100% | 47,152 psi | 74% | 3179 fps | 98.5% |
| Baschieri & Pellagri 107 | <<locked>> | 86% | 56,710 psi | 89% | 3186 fps | 99.7% |
| Bofors RP3 | <<locked>> | 90% | 54,955 psi | 86% | 3153 fps | 100% |
| Bofors RP7 | <<locked>> | 94% | 55,129 psi | 86% | 3123 fps | 97.1% |
| Hodgdon Benchmark | <<locked>> | 84% | 57,188 psi | 90% | 3104 fps | 100% |
| Hodgdon BL-C2 | <<locked>> | 84% | 55,317 psi | 87% | 3150 fps | 100% |
| Hodgdon CFE223 | <<locked>> | 82% | 57,377 psi | 90% | 3258 fps | 99.9% |
| Hodgdon H380 | <<locked>> | 90% | 55,898 psi | 88% | 3166 fps | 99.3% |
| Hodgdon H414 | <<locked>> | 96% | 56,057 psi | 88% | 3225 fps | 97.9% |
| Hodgdon H4350 | <<locked>> | 94% | 56,434 psi | 88% | 3182 fps | 96.7% |
| Hodgdon H4895 | <<locked>> | 86% | 57,406 psi | 90% | 3186 fps | 100% |
| Hodgdon Hybrid 100Vᴾ | <<locked>> | 100% | 54,331 psi | 85% | 3153 fps | 100% |
| Hodgdon LEVERevolution | <<locked>> | 88% | 57,159 psi | 90% | 3219 fps | 100% |
| Hodgdon Superformance | <<locked>> | 96% | 56,985 psi | 89% | 3264 fps | 97.8% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 35,447 psi | 56% | 1962 fps | 100% |
| Hodgdon VARGET | <<locked>> | 86% | 54,926 psi | 86% | 3130 fps | 100% |
| IMR 3031 | <<locked>> | 86% | 57,595 psi | 90% | 3166 fps | 100% |
| IMR 4064 | <<locked>> | 90% | 57,421 psi | 90% | 3156 fps | 99.9% |
| IMR 4166 Enduron | <<locked>> | 88% | 56,971 psi | 89% | 3130 fps | 97.9% |
| IMR 4350 | <<locked>> | 98% | 55,811 psi | 87% | 3153 fps | 97.3% |
| IMR 4451 Enduron | <<locked>> | 94% | 57,043 psi | 89% | 3156 fps | 97.9% |
| IMR 4831ᴾ | <<locked>> | 100% | 57,682 psi | 90% | 3219 fps | 99.8% |
| IMR 4895 | <<locked>> | 88% | 56,376 psi | 88% | 3196 fps | 100% |
| IMR 8208 XBR | <<locked>> | 84% | 55,448 psi | 87% | 3117 fps | 100% |
| Lovex D073.6 | <<locked>> | 86% | 56,594 psi | 89% | 3143 fps | 100% |
| Lovex S060 | <<locked>> | 86% | 56,130 psi | 88% | 3097 fps | 100% |
| Lovex S062 | <<locked>> | 90% | 57,188 psi | 90% | 3150 fps | 100% |
| Lovex S065 | <<locked>> | 96% | 56,289 psi | 88% | 3146 fps | 98.9% |
| Lovex S070 | <<locked>> | 98% | 57,595 psi | 90% | 3189 fps | 98.3% |
| Norma 201 | <<locked>> | 86% | 55,201 psi | 87% | 3110 fps | 100% |
| Norma 202 | <<locked>> | 86% | 55,796 psi | 87% | 3110 fps | 100% |
| Norma 203B | <<locked>> | 90% | 57,711 psi | 90% | 3205 fps | 100% |
| Norma 204 | <<locked>> | 98% | 56,594 psi | 89% | 3205 fps | 96.2% |
| Norma URP | <<locked>> | 98% | 55,883 psi | 88% | 3215 fps | 99.6% |
| Ramshot Big Game | <<locked>> | 88% | 55,129 psi | 86% | 3176 fps | 99.9% |
| Ramshot Hunter | <<locked>> | 98% | 54,795 psi | 86% | 3209 fps | 98.5% |
| Ramshot TAC | <<locked>> | 84% | 55,825 psi | 87% | 3133 fps | 98.9% |
| Ramshot Wild Boar | <<locked>> | 84% | 55,695 psi | 87% | 3156 fps | 99.9% |
| Ramshot X-Terminator | <<locked>> | 82% | 56,188 psi | 88% | 3114 fps | 99.9% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 36,085 psi | 57% | 2011 fps | 100% |
| ReloadSwiss RS 50 | <<locked>> | 90% | 56,347 psi | 88% | 3150 fps | 98.4% |
| ReloadSwiss RS 52 | <<locked>> | 86% | 55,608 psi | 87% | 3235 fps | 99.8% |
| ReloadSwiss RS 60 | <<locked>> | 92% | 55,550 psi | 87% | 3271 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 98% | 57,072 psi | 89% | 3251 fps | 99.6% |
| ReloadSwiss RS 70 | <<locked>> | 98% | 56,492 psi | 89% | 3287 fps | 99.5% |
| Rottweil R 901 | <<locked>> | 84% | 55,941 psi | 88% | 3094 fps | 100% |
| Rottweil R 902 | <<locked>> | 88% | 55,825 psi | 87% | 3110 fps | 100% |
| Rottweil R 903 | <<locked>> | 92% | 54,824 psi | 86% | 3143 fps | 100% |
| Rottweil R 907 | <<locked>> | 94% | 55,129 psi | 86% | 3123 fps | 97.1% |
| Shooters World Long Rifle | <<locked>> | 96% | 56,289 psi | 88% | 3146 fps | 98.9% |
| Shooters World Match Rifle | <<locked>> | 86% | 56,594 psi | 89% | 3143 fps | 100% |
| Shooters World Precision | <<locked>> | 90% | 57,188 psi | 90% | 3150 fps | 100% |
| Shooters World SW4350 | <<locked>> | 98% | 57,595 psi | 90% | 3189 fps | 98.3% |
| SNPE Vectan SP 11 | <<locked>> | 92% | 57,029 psi | 89% | 3215 fps | 100% |
| SNPE Vectan SP 7 | <<locked>> | 84% | 54,389 psi | 85% | 3110 fps | 99.1% |
| SNPE Vectan SP 9 | <<locked>> | 86% | 55,114 psi | 86% | 3136 fps | 99.9% |
| SNPE Vectan Tubal 3000 | <<locked>> | 86% | 56,463 psi | 88% | 3048 fps | 100% |
| SNPE Vectan Tubal 5000 | <<locked>> | 92% | 57,305 psi | 90% | 3048 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 96% | 56,710 psi | 89% | 3097 fps | 97.9% |
| Somchem S321 | <<locked>> | 82% | 56,811 psi | 89% | 3150 fps | 100% |
| Somchem S335 | <<locked>> | 86% | 56,028 psi | 88% | 3041 fps | 100% |
| Somchem S341 | <<locked>> | 84% | 53,983 psi | 85% | 3100 fps | 99.8% |
| Somchem S355 | <<locked>> | 92% | 55,158 psi | 86% | 3143 fps | 100% |
| Somchem S365ᴾ | <<locked>> | 100% | 54,143 psi | 85% | 3215 fps | 100% |
| Somchem S385ᴾ | <<locked>> | 100% | 50,198 psi | 79% | 3084 fps | 96.1% |
| Vihtavuori N130 | <<locked>> | 82% | 56,217 psi | 88% | 3005 fps | 100% |
| Vihtavuori N133 | <<locked>> | 86% | 56,840 psi | 89% | 3028 fps | 100% |
| Vihtavuori N135 | <<locked>> | 88% | 55,593 psi | 87% | 3071 fps | 100% |
| Vihtavuori N140 | <<locked>> | 88% | 56,565 psi | 89% | 3091 fps | 100% |
| Vihtavuori N150 | <<locked>> | 94% | 57,000 psi | 89% | 3123 fps | 100% |
| Vihtavuori N160 | <<locked>> | 96% | 54,694 psi | 86% | 3153 fps | 99.4% |
| Vihtavuori N530 | <<locked>> | 84% | 56,072 psi | 88% | 3117 fps | 100% |
| Vihtavuori N540 | <<locked>> | 88% | 54,795 psi | 86% | 3084 fps | 100% |
| Vihtavuori N550 | <<locked>> | 98% | 57,653 psi | 90% | 3219 fps | 99.6% |
| Vihtavuori N555ᴾ | <<locked>> | 100% | 45,992 psi | 72% | 3077 fps | 98.9% |
| Winchester 6.5 StaBALL | <<locked>> | 96% | 55,100 psi | 86% | 3130 fps | 100% |
| Winchester 748 | <<locked>> | 84% | 56,492 psi | 89% | 3173 fps | 100% |
| Winchester 760 | <<locked>> | 96% | 56,449 psi | 88% | 3228 fps | 98% |
| Winchester StaBALL HDᴾ | <<locked>> | 100% | 37,202 psi | 58% | 2995 fps | 98.9% |
| Winchester StaBALL Match | <<locked>> | 86% | 55,259 psi | 87% | 3150 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% | 50,546 psi | 79% | 2959 fps | 100% |
| Accurate 2495 | <<locked>> | 80% | 42,946 psi | 67% | 2867 fps | 100% |
| Accurate 2520 | <<locked>> | 80% | 50,604 psi | 79% | 3041 fps | 100% |
| Accurate 2700 | <<locked>> | 84% | 48,428 psi | 76% | 2959 fps | 95.4% |
| Accurate 3100 | <<locked>> | 98% | 40,756 psi | 64% | 2897 fps | 95.3% |
| Accurate 4064 | <<locked>> | 80% | 40,611 psi | 64% | 2861 fps | 100% |
| Accurate 4350 | <<locked>> | 86% | 37,217 psi | 58% | 2844 fps | 96% |
| ADI AR 2206H | <<locked>> | 80% | 46,789 psi | 73% | 2995 fps | 99.2% |
| ADI AR 2208 | <<locked>> | 80% | 39,508 psi | 62% | 2825 fps | 97.3% |
| ADI Benchmark 8208 | <<locked>> | 80% | 48,936 psi | 77% | 3009 fps | 99.9% |
| Alliant AR-Comp | <<locked>> | 80% | 49,516 psi | 78% | 2989 fps | 100% |
| Alliant Power Pro 2000-MR | <<locked>> | 80% | 42,931 psi | 67% | 3031 fps | 98.1% |
| Alliant Reloder- TS 15.5 | <<locked>> | 80% | 39,392 psi | 62% | 2851 fps | 98.6% |
| Alliant Reloder-15 | <<locked>> | 80% | 42,380 psi | 66% | 2923 fps | 98.1% |
| Alliant Reloder-16 | <<locked>> | 84% | 34,679 psi | 54% | 2795 fps | 95.1% |
| Alliant Reloder-17 | 43.4 gr | 80% | 34,113 psi | 53% | 2808 fps | 96.8% |
| Alliant Reloder-23 | <<locked>> | 92% | 31,952 psi | 50% | 2740 fps | 95.7% |
| Alliant Reloder-26 | <<locked>> | 94% | 37,565 psi | 59% | 2949 fps | 95.5% |
| Baschieri & Pellagri 107 | <<locked>> | 80% | 46,195 psi | 72% | 2999 fps | 98.5% |
| Bofors RP3 | <<locked>> | 80% | 39,015 psi | 61% | 2851 fps | 98.7% |
| Bofors RP7 | <<locked>> | 90% | 48,573 psi | 76% | 3002 fps | 95.7% |
| Hodgdon Benchmark | <<locked>> | 80% | 50,314 psi | 79% | 2989 fps | 100% |
| Hodgdon BL-C2 | <<locked>> | 80% | 48,124 psi | 75% | 3028 fps | 100% |
| Hodgdon CFE223 | <<locked>> | 80% | 53,461 psi | 84% | 3192 fps | 99.7% |
| Hodgdon H380 | <<locked>> | 80% | 39,987 psi | 63% | 2858 fps | 96.3% |
| Hodgdon H414 | <<locked>> | 90% | 45,629 psi | 72% | 3028 fps | 95.6% |
| Hodgdon H4350 | <<locked>> | 90% | 49,487 psi | 78% | 3058 fps | 95.1% |
| Hodgdon H4895 | <<locked>> | 80% | 47,239 psi | 74% | 3009 fps | 99.6% |
| Hodgdon Hybrid 100V | <<locked>> | 84% | 31,778 psi | 50% | 2680 fps | 95.9% |
| Hodgdon LEVERevolution | <<locked>> | 80% | 43,381 psi | 68% | 2972 fps | 99.4% |
| Hodgdon Superformance | 51.6 gr | 90% | 45,730 psi | 72% | 3054 fps | 95.1% |
| Hodgdon TrailBoss | <<locked>> | 80% | 26,281 psi | 41% | 1755 fps | 100% |
| Hodgdon VARGET | <<locked>> | 80% | 45,179 psi | 71% | 2953 fps | 99.3% |
| IMR 3031 | <<locked>> | 80% | 47,166 psi | 74% | 3005 fps | 100% |
| IMR 4064 | <<locked>> | 80% | 41,466 psi | 65% | 2861 fps | 98% |
| IMR 4166 Enduron | <<locked>> | 80% | 44,222 psi | 69% | 2890 fps | 95.1% |
| IMR 4350 | <<locked>> | 92% | 46,006 psi | 72% | 2972 fps | 95% |
| IMR 4451 Enduron | <<locked>> | 86% | 44,353 psi | 70% | 2920 fps | 95% |
| IMR 4831 | <<locked>> | 86% | 35,911 psi | 56% | 2795 fps | 95.6% |
| IMR 4895 | <<locked>> | 80% | 43,439 psi | 68% | 2956 fps | 98.8% |
| IMR 8208 XBR | <<locked>> | 80% | 48,936 psi | 77% | 3009 fps | 99.9% |
| Lovex D073.6 | <<locked>> | 80% | 45,963 psi | 72% | 2969 fps | 100% |
| Lovex S060 | <<locked>> | 80% | 46,369 psi | 73% | 2923 fps | 99.2% |
| Lovex S062 | <<locked>> | 80% | 41,379 psi | 65% | 2864 fps | 99.3% |
| Lovex S065 | <<locked>> | 86% | 41,220 psi | 65% | 2858 fps | 95.8% |
| Lovex S070 | <<locked>> | 90% | 44,512 psi | 70% | 2946 fps | 95.5% |
| Norma 201 | <<locked>> | 80% | 45,600 psi | 71% | 2943 fps | 99.7% |
| Norma 202 | <<locked>> | 80% | 46,093 psi | 72% | 2949 fps | 100% |
| Norma 203B | <<locked>> | 80% | 41,742 psi | 65% | 2910 fps | 98.5% |
| Norma 204 | <<locked>> | 96% | 52,692 psi | 83% | 3136 fps | 95.3% |
| Norma URP | <<locked>> | 84% | 34,983 psi | 55% | 2785 fps | 95% |
| Ramshot Big Game | <<locked>> | 80% | 41,626 psi | 65% | 2923 fps | 98.3% |
| Ramshot Hunter | <<locked>> | 90% | 41,640 psi | 65% | 2953 fps | 95.4% |
| Ramshot TAC | <<locked>> | 80% | 48,863 psi | 77% | 3012 fps | 97.9% |
| Ramshot Wild Boar | <<locked>> | 80% | 48,573 psi | 76% | 3031 fps | 99.4% |
| Ramshot X-Terminator | <<locked>> | 80% | 52,605 psi | 82% | 3054 fps | 99.7% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 26,672 psi | 42% | 1798 fps | 100% |
| ReloadSwiss RS 50 | <<locked>> | 82% | 43,120 psi | 68% | 2900 fps | 95.5% |
| ReloadSwiss RS 52 | <<locked>> | 80% | 44,976 psi | 70% | 3038 fps | 98.6% |
| ReloadSwiss RS 60 | <<locked>> | 80% | 36,376 psi | 57% | 2884 fps | 99.5% |
| ReloadSwiss RS 62 | <<locked>> | 86% | 37,043 psi | 58% | 2861 fps | 95.5% |
| ReloadSwiss RS 70 | 48.5 gr | 88% | 39,682 psi | 62% | 2940 fps | 95.8% |
| Rottweil R 901 | <<locked>> | 80% | 49,371 psi | 77% | 2986 fps | 100% |
| Rottweil R 902 | <<locked>> | 80% | 43,323 psi | 68% | 2887 fps | 99.5% |
| Rottweil R 903 | <<locked>> | 80% | 36,637 psi | 57% | 2785 fps | 97.8% |
| Rottweil R 907 | <<locked>> | 90% | 48,573 psi | 76% | 3002 fps | 95.7% |
| Shooters World Long Rifle | <<locked>> | 86% | 41,220 psi | 65% | 2858 fps | 95.8% |
| Shooters World Match Rifle | <<locked>> | 80% | 45,963 psi | 72% | 2969 fps | 100% |
| Shooters World Precision | <<locked>> | 80% | 41,379 psi | 65% | 2864 fps | 99.3% |
| Shooters World SW4350 | <<locked>> | 90% | 44,512 psi | 70% | 2946 fps | 95.5% |
| SNPE Vectan SP 11 | <<locked>> | 80% | 37,869 psi | 59% | 2844 fps | 97.4% |
| SNPE Vectan SP 7 | <<locked>> | 80% | 47,253 psi | 74% | 2986 fps | 98% |
| SNPE Vectan SP 9 | <<locked>> | 80% | 45,208 psi | 71% | 2959 fps | 99% |
| SNPE Vectan Tubal 3000 | <<locked>> | 80% | 46,804 psi | 73% | 2890 fps | 100% |
| SNPE Vectan Tubal 5000 | <<locked>> | 80% | 39,044 psi | 61% | 2740 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 88% | 43,526 psi | 68% | 2858 fps | 95% |
| Somchem S321 | <<locked>> | 80% | 53,084 psi | 83% | 3091 fps | 100% |
| Somchem S335 | <<locked>> | 80% | 46,586 psi | 73% | 2890 fps | 100% |
| Somchem S341 | <<locked>> | 80% | 47,007 psi | 74% | 2979 fps | 99.2% |
| Somchem S355 | <<locked>> | 80% | 37,536 psi | 59% | 2799 fps | 97.9% |
| Somchem S365 | <<locked>> | 80% | 27,064 psi | 42% | 2592 fps | 95% |
| Somchem S385 | <<locked>> | 98% | 46,717 psi | 73% | 3015 fps | 95.2% |
| Vihtavuori N130 | <<locked>> | 80% | 52,794 psi | 83% | 2956 fps | 100% |
| Vihtavuori N133 | <<locked>> | 80% | 47,253 psi | 74% | 2884 fps | 100% |
| Vihtavuori N135 | <<locked>> | 80% | 42,946 psi | 67% | 2867 fps | 100% |
| Vihtavuori N140 | <<locked>> | 80% | 43,598 psi | 68% | 2877 fps | 100% |
| Vihtavuori N150 | <<locked>> | 80% | 35,650 psi | 56% | 2726 fps | 98.6% |
| Vihtavuori N160 | <<locked>> | 84% | 36,390 psi | 57% | 2789 fps | 95.5% |
| Vihtavuori N530 | <<locked>> | 80% | 48,994 psi | 77% | 3002 fps | 99.9% |
| Vihtavuori N540 | <<locked>> | 80% | 42,177 psi | 66% | 2864 fps | 100% |
| Vihtavuori N550 | <<locked>> | 84% | 35,955 psi | 56% | 2789 fps | 95.1% |
| Vihtavuori N555 | <<locked>> | 92% | 34,809 psi | 55% | 2828 fps | 95.9% |
| Winchester 6.5 StaBALL | <<locked>> | 80% | 31,618 psi | 50% | 2638 fps | 96.1% |
| Winchester 748 | <<locked>> | 80% | 49,095 psi | 77% | 3051 fps | 100% |
| Winchester 760 | <<locked>> | 90% | 45,934 psi | 72% | 3035 fps | 95.7% |
| Winchester StaBALL HD | <<locked>> | 94% | 30,327 psi | 48% | 2769 fps | 95.4% |
| Winchester StaBALL Match | <<locked>> | 80% | 44,831 psi | 70% | 2963 fps | 99.4% |
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 97 powders for .255 GS loaded with the .257 | 100gr | Osprey Virtus. Alliant Power Pro 2000-MR delivers the highest muzzle velocity at 3,307 fps; across all powders the maximum-charge window runs from 1,962 fps to 3,307 fps. Accurate 3100 gives the best case fill at 100 %, and 97 of the 97 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 1:10.0 twist; slower twists will usually not stabilise this weight. Accurate 3100, Alliant Reloder-23, Alliant Reloder-26 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, Hodgdon Superformance, Alliant Reloder-17 rank at the top here: for .255 GS with the .257 | 100gr | Osprey Virtus 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.