Load Specifications
Load data in caliber .255 GS with .257 | 100gr | Barnes TSX BT 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 60, ReloadSwiss RS 70 and Hodgdon Superformance.
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% | 57,232 psi | 90% | 3061 fps | 100% |
| Accurate 2495 | <<locked>> | 88% | 55,840 psi | 88% | 3077 fps | 100% |
| Accurate 2520 | <<locked>> | 82% | 54,186 psi | 85% | 3097 fps | 100% |
| Accurate 2700 | <<locked>> | 88% | 55,376 psi | 87% | 3084 fps | 96.9% |
| Accurate 3100ᴾ | <<locked>> | 100% | 43,540 psi | 68% | 2956 fps | 96.1% |
| Accurate 4064 | <<locked>> | 90% | 56,014 psi | 88% | 3130 fps | 100% |
| Accurate 4350 | <<locked>> | 98% | 56,985 psi | 89% | 3228 fps | 99.7% |
| ADI AR 2206H | <<locked>> | 86% | 56,594 psi | 89% | 3169 fps | 100% |
| ADI AR 2208 | <<locked>> | 90% | 54,346 psi | 85% | 3117 fps | 99.7% |
| ADI Benchmark 8208 | <<locked>> | 84% | 55,593 psi | 87% | 3120 fps | 100% |
| Alliant AR-Comp | <<locked>> | 84% | 56,434 psi | 88% | 3091 fps | 100% |
| Alliant Power Pro 2000-MR | <<locked>> | 88% | 56,956 psi | 89% | 3304 fps | 99.9% |
| Alliant Reloder- TS 15.5 | <<locked>> | 90% | 54,418 psi | 85% | 3140 fps | 100% |
| Alliant Reloder-15 | <<locked>> | 88% | 54,781 psi | 86% | 3159 fps | 99.8% |
| Alliant Reloder-16 | <<locked>> | 98% | 54,491 psi | 85% | 3232 fps | 99.7% |
| Alliant Reloder-17 | <<locked>> | 94% | 55,811 psi | 87% | 3271 fps | 100% |
| Alliant Reloder-23ᴾ | <<locked>> | 100% | 41,437 psi | 65% | 2992 fps | 99% |
| Alliant Reloder-26ᴾ | <<locked>> | 100% | 46,992 psi | 74% | 3176 fps | 98.5% |
| Baschieri & Pellagri 107 | <<locked>> | 86% | 56,884 psi | 89% | 3189 fps | 99.7% |
| Bofors RP3 | <<locked>> | 90% | 55,129 psi | 86% | 3153 fps | 100% |
| Bofors RP7 | <<locked>> | 94% | 54,926 psi | 86% | 3120 fps | 97.1% |
| Hodgdon Benchmark | <<locked>> | 84% | 57,029 psi | 89% | 3100 fps | 100% |
| Hodgdon BL-C2 | <<locked>> | 84% | 55,129 psi | 86% | 3146 fps | 100% |
| Hodgdon CFE223 | <<locked>> | 82% | 57,203 psi | 90% | 3258 fps | 99.9% |
| Hodgdon H380 | <<locked>> | 90% | 56,086 psi | 88% | 3169 fps | 99.3% |
| Hodgdon H414 | <<locked>> | 96% | 55,927 psi | 88% | 3222 fps | 97.9% |
| Hodgdon H4350 | <<locked>> | 94% | 56,275 psi | 88% | 3179 fps | 96.7% |
| Hodgdon H4895 | <<locked>> | 86% | 57,188 psi | 90% | 3182 fps | 100% |
| Hodgdon Hybrid 100Vᴾ | <<locked>> | 100% | 54,157 psi | 85% | 3150 fps | 100% |
| Hodgdon LEVERevolution | <<locked>> | 88% | 57,000 psi | 89% | 3215 fps | 100% |
| Hodgdon Superformance | <<locked>> | 96% | 56,826 psi | 89% | 3261 fps | 97.8% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 35,520 psi | 56% | 1965 fps | 100% |
| Hodgdon VARGET | <<locked>> | 86% | 54,781 psi | 86% | 3127 fps | 100% |
| IMR 3031 | <<locked>> | 86% | 57,406 psi | 90% | 3163 fps | 100% |
| IMR 4064 | <<locked>> | 90% | 57,246 psi | 90% | 3153 fps | 99.9% |
| IMR 4166 Enduron | <<locked>> | 88% | 57,145 psi | 90% | 3133 fps | 98% |
| IMR 4350 | <<locked>> | 98% | 55,637 psi | 87% | 3150 fps | 97.3% |
| IMR 4451 Enduron | <<locked>> | 94% | 56,913 psi | 89% | 3156 fps | 97.9% |
| IMR 4831ᴾ | <<locked>> | 100% | 57,508 psi | 90% | 3219 fps | 99.7% |
| IMR 4895 | <<locked>> | 88% | 56,217 psi | 88% | 3192 fps | 100% |
| IMR 8208 XBR | <<locked>> | 84% | 55,593 psi | 87% | 3120 fps | 100% |
| Lovex D073.6 | <<locked>> | 86% | 56,420 psi | 88% | 3140 fps | 100% |
| Lovex S060 | <<locked>> | 86% | 55,941 psi | 88% | 3094 fps | 99.9% |
| Lovex S062 | <<locked>> | 90% | 57,000 psi | 89% | 3146 fps | 100% |
| Lovex S065 | <<locked>> | 96% | 56,478 psi | 89% | 3150 fps | 98.9% |
| Lovex S070 | <<locked>> | 98% | 57,421 psi | 90% | 3186 fps | 98.2% |
| Norma 201 | <<locked>> | 86% | 54,969 psi | 86% | 3107 fps | 100% |
| Norma 202 | <<locked>> | 86% | 55,956 psi | 88% | 3114 fps | 100% |
| Norma 203B | <<locked>> | 88% | 54,012 psi | 85% | 3143 fps | 99.9% |
| Norma 204 | <<locked>> | 98% | 56,478 psi | 89% | 3202 fps | 96.1% |
| Norma URP | <<locked>> | 98% | 55,680 psi | 87% | 3212 fps | 99.6% |
| Ramshot Big Game | <<locked>> | 88% | 54,984 psi | 86% | 3173 fps | 99.9% |
| Ramshot Hunter | <<locked>> | 98% | 54,607 psi | 86% | 3205 fps | 98.4% |
| Ramshot TAC | <<locked>> | 84% | 55,637 psi | 87% | 3130 fps | 98.9% |
| Ramshot Wild Boar | <<locked>> | 84% | 55,492 psi | 87% | 3153 fps | 99.9% |
| Ramshot X-Terminator | <<locked>> | 82% | 56,362 psi | 88% | 3117 fps | 99.9% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 35,868 psi | 56% | 2008 fps | 100% |
| ReloadSwiss RS 50 | <<locked>> | 90% | 56,159 psi | 88% | 3146 fps | 98.3% |
| ReloadSwiss RS 52 | <<locked>> | 86% | 55,434 psi | 87% | 3232 fps | 99.8% |
| ReloadSwiss RS 60 | <<locked>> | 92% | 55,376 psi | 87% | 3271 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 98% | 56,884 psi | 89% | 3248 fps | 99.6% |
| ReloadSwiss RS 70 | <<locked>> | 98% | 56,347 psi | 88% | 3284 fps | 99.5% |
| Rottweil R 901 | <<locked>> | 84% | 55,782 psi | 87% | 3091 fps | 100% |
| Rottweil R 902 | <<locked>> | 88% | 55,651 psi | 87% | 3110 fps | 100% |
| Rottweil R 903 | <<locked>> | 92% | 54,984 psi | 86% | 3143 fps | 100% |
| Rottweil R 907 | <<locked>> | 94% | 54,926 psi | 86% | 3120 fps | 97.1% |
| Shooters World Long Rifle | <<locked>> | 96% | 56,478 psi | 89% | 3150 fps | 98.9% |
| Shooters World Match Rifle | <<locked>> | 86% | 56,420 psi | 88% | 3140 fps | 100% |
| Shooters World Precision | <<locked>> | 90% | 57,000 psi | 89% | 3146 fps | 100% |
| Shooters World SW4350 | <<locked>> | 98% | 57,421 psi | 90% | 3186 fps | 98.2% |
| SNPE Vectan SP 11 | <<locked>> | 92% | 56,855 psi | 89% | 3212 fps | 100% |
| SNPE Vectan SP 7 | <<locked>> | 84% | 54,186 psi | 85% | 3107 fps | 99.1% |
| SNPE Vectan SP 9 | <<locked>> | 86% | 54,969 psi | 86% | 3133 fps | 99.9% |
| SNPE Vectan Tubal 3000 | <<locked>> | 86% | 56,623 psi | 89% | 3048 fps | 100% |
| SNPE Vectan Tubal 5000 | <<locked>> | 92% | 57,130 psi | 90% | 3045 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 96% | 56,942 psi | 89% | 3100 fps | 97.9% |
| Somchem S321 | <<locked>> | 82% | 56,652 psi | 89% | 3146 fps | 100% |
| Somchem S335 | <<locked>> | 86% | 55,869 psi | 88% | 3038 fps | 100% |
| Somchem S341 | <<locked>> | 84% | 54,143 psi | 85% | 3104 fps | 99.9% |
| Somchem S355 | <<locked>> | 92% | 55,274 psi | 87% | 3146 fps | 100% |
| Somchem S365ᴾ | <<locked>> | 100% | 53,998 psi | 85% | 3212 fps | 100% |
| Somchem S385ᴾ | <<locked>> | 100% | 50,024 psi | 78% | 3081 fps | 96.1% |
| Vihtavuori N130 | <<locked>> | 82% | 55,999 psi | 88% | 3005 fps | 100% |
| Vihtavuori N133 | <<locked>> | 86% | 57,000 psi | 89% | 3031 fps | 100% |
| Vihtavuori N135 | <<locked>> | 88% | 55,767 psi | 87% | 3074 fps | 100% |
| Vihtavuori N140 | <<locked>> | 88% | 56,376 psi | 88% | 3087 fps | 100% |
| Vihtavuori N150 | <<locked>> | 94% | 56,811 psi | 89% | 3120 fps | 100% |
| Vihtavuori N160 | <<locked>> | 96% | 54,491 psi | 85% | 3150 fps | 99.4% |
| Vihtavuori N530 | <<locked>> | 84% | 55,869 psi | 88% | 3117 fps | 100% |
| Vihtavuori N540 | <<locked>> | 88% | 54,621 psi | 86% | 3081 fps | 100% |
| Vihtavuori N550 | <<locked>> | 98% | 57,493 psi | 90% | 3215 fps | 99.6% |
| Vihtavuori N555ᴾ | <<locked>> | 100% | 45,861 psi | 72% | 3074 fps | 98.9% |
| Winchester 6.5 StaBALL | <<locked>> | 96% | 54,940 psi | 86% | 3127 fps | 100% |
| Winchester 748 | <<locked>> | 84% | 56,333 psi | 88% | 3169 fps | 100% |
| Winchester 760 | <<locked>> | 96% | 56,260 psi | 88% | 3225 fps | 98% |
| Winchester StaBALL HDᴾ | <<locked>> | 100% | 37,130 psi | 58% | 2992 fps | 98.9% |
| Winchester StaBALL Match | <<locked>> | 86% | 55,114 psi | 86% | 3146 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% | 50,328 psi | 79% | 2959 fps | 100% |
| Accurate 2495 | <<locked>> | 80% | 42,728 psi | 67% | 2864 fps | 100% |
| Accurate 2520 | <<locked>> | 80% | 50,430 psi | 79% | 3038 fps | 100% |
| Accurate 2700 | <<locked>> | 84% | 48,240 psi | 76% | 2956 fps | 95.3% |
| Accurate 3100 | <<locked>> | 98% | 40,596 psi | 64% | 2894 fps | 95.2% |
| Accurate 4064 | <<locked>> | 80% | 40,451 psi | 63% | 2858 fps | 100% |
| Accurate 4350 | <<locked>> | 84% | 34,534 psi | 54% | 2776 fps | 95% |
| ADI AR 2206H | <<locked>> | 80% | 46,630 psi | 73% | 2992 fps | 99.2% |
| ADI AR 2208 | <<locked>> | 80% | 39,595 psi | 62% | 2825 fps | 97.3% |
| ADI Benchmark 8208 | <<locked>> | 80% | 48,747 psi | 76% | 3002 fps | 99.9% |
| Alliant AR-Comp | <<locked>> | 80% | 49,284 psi | 77% | 2986 fps | 100% |
| Alliant Power Pro 2000-MR | <<locked>> | 80% | 42,786 psi | 67% | 3028 fps | 98% |
| Alliant Reloder- TS 15.5 | <<locked>> | 80% | 39,247 psi | 62% | 2848 fps | 98.6% |
| Alliant Reloder-15 | <<locked>> | 80% | 42,206 psi | 66% | 2920 fps | 98.1% |
| Alliant Reloder-16 | <<locked>> | 84% | 34,548 psi | 54% | 2792 fps | 95% |
| Alliant Reloder-17 | <<locked>> | 80% | 33,982 psi | 53% | 2805 fps | 96.7% |
| Alliant Reloder-23 | <<locked>> | 92% | 32,068 psi | 50% | 2746 fps | 95.8% |
| Alliant Reloder-26 | <<locked>> | 94% | 37,710 psi | 59% | 2956 fps | 95.6% |
| Baschieri & Pellagri 107 | <<locked>> | 80% | 46,050 psi | 72% | 2995 fps | 98.4% |
| Bofors RP3 | <<locked>> | 80% | 38,885 psi | 61% | 2844 fps | 98.6% |
| Bofors RP7 | <<locked>> | 90% | 48,414 psi | 76% | 2999 fps | 95.6% |
| Hodgdon Benchmark | <<locked>> | 80% | 50,459 psi | 79% | 2992 fps | 100% |
| Hodgdon BL-C2 | <<locked>> | 80% | 47,964 psi | 75% | 3025 fps | 100% |
| Hodgdon CFE223 | <<locked>> | 80% | 53,272 psi | 83% | 3189 fps | 99.7% |
| Hodgdon H380 | <<locked>> | 80% | 39,827 psi | 62% | 2854 fps | 96.2% |
| Hodgdon H414 | <<locked>> | 90% | 45,759 psi | 72% | 3031 fps | 95.7% |
| Hodgdon H4350 | <<locked>> | 90% | 49,632 psi | 78% | 3061 fps | 95.1% |
| Hodgdon H4895 | <<locked>> | 80% | 47,065 psi | 74% | 3005 fps | 99.6% |
| Hodgdon Hybrid 100V | <<locked>> | 84% | 31,662 psi | 50% | 2677 fps | 95.8% |
| Hodgdon LEVERevolution | <<locked>> | 80% | 43,236 psi | 68% | 2972 fps | 99.4% |
| Hodgdon Superformance | 51.5 gr | 90% | 45,571 psi | 71% | 3051 fps | 95% |
| Hodgdon TrailBoss | <<locked>> | 80% | 26,324 psi | 41% | 1755 fps | 100% |
| Hodgdon VARGET | <<locked>> | 80% | 45,310 psi | 71% | 2956 fps | 99.3% |
| IMR 3031 | <<locked>> | 80% | 46,978 psi | 74% | 2999 fps | 100% |
| IMR 4064 | <<locked>> | 80% | 41,582 psi | 65% | 2864 fps | 98% |
| IMR 4166 Enduron | <<locked>> | 80% | 44,077 psi | 69% | 2890 fps | 95.1% |
| IMR 4350 | <<locked>> | 94% | 49,110 psi | 77% | 3031 fps | 95.8% |
| IMR 4451 Enduron | <<locked>> | 86% | 44,483 psi | 70% | 2923 fps | 95% |
| IMR 4831 | <<locked>> | 86% | 35,810 psi | 56% | 2792 fps | 95.6% |
| IMR 4895 | <<locked>> | 80% | 43,279 psi | 68% | 2953 fps | 98.8% |
| IMR 8208 XBR | <<locked>> | 80% | 48,747 psi | 76% | 3002 fps | 99.9% |
| Lovex D073.6 | <<locked>> | 80% | 45,818 psi | 72% | 2966 fps | 100% |
| Lovex S060 | <<locked>> | 80% | 46,485 psi | 73% | 2927 fps | 99.2% |
| Lovex S062 | <<locked>> | 80% | 41,495 psi | 65% | 2867 fps | 99.3% |
| Lovex S065 | <<locked>> | 86% | 41,060 psi | 64% | 2854 fps | 95.7% |
| Lovex S070 | <<locked>> | 90% | 44,382 psi | 70% | 2943 fps | 95.4% |
| Norma 201 | <<locked>> | 80% | 45,440 psi | 71% | 2940 fps | 99.7% |
| Norma 202 | <<locked>> | 80% | 45,905 psi | 72% | 2946 fps | 100% |
| Norma 203B | <<locked>> | 80% | 41,597 psi | 65% | 2904 fps | 98.4% |
| Norma 204 | <<locked>> | 96% | 52,881 psi | 83% | 3140 fps | 95.3% |
| Norma URP | <<locked>> | 86% | 37,246 psi | 58% | 2844 fps | 95.9% |
| Ramshot Big Game | <<locked>> | 80% | 41,466 psi | 65% | 2920 fps | 98.3% |
| Ramshot Hunter | <<locked>> | 90% | 41,785 psi | 65% | 2953 fps | 95.4% |
| Ramshot TAC | <<locked>> | 80% | 48,704 psi | 76% | 3009 fps | 97.8% |
| Ramshot Wild Boar | <<locked>> | 80% | 48,428 psi | 76% | 3031 fps | 99.4% |
| Ramshot X-Terminator | <<locked>> | 80% | 52,750 psi | 83% | 3058 fps | 99.7% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 26,731 psi | 42% | 1798 fps | 100% |
| ReloadSwiss RS 50 | <<locked>> | 82% | 42,989 psi | 67% | 2900 fps | 95.5% |
| ReloadSwiss RS 52 | <<locked>> | 80% | 44,788 psi | 70% | 3035 fps | 98.5% |
| ReloadSwiss RS 60 | 43.3 gr | 80% | 36,230 psi | 57% | 2884 fps | 99.5% |
| ReloadSwiss RS 62 | <<locked>> | 86% | 36,912 psi | 58% | 2858 fps | 95.5% |
| ReloadSwiss RS 70 | 48.4 gr | 88% | 39,552 psi | 62% | 2940 fps | 95.7% |
| Rottweil R 901 | <<locked>> | 80% | 49,182 psi | 77% | 2982 fps | 100% |
| Rottweil R 902 | <<locked>> | 80% | 43,134 psi | 68% | 2884 fps | 99.5% |
| Rottweil R 903 | <<locked>> | 80% | 36,477 psi | 57% | 2782 fps | 97.8% |
| Rottweil R 907 | <<locked>> | 90% | 48,414 psi | 76% | 2999 fps | 95.6% |
| Shooters World Long Rifle | <<locked>> | 86% | 41,060 psi | 64% | 2854 fps | 95.7% |
| Shooters World Match Rifle | <<locked>> | 80% | 45,818 psi | 72% | 2966 fps | 100% |
| Shooters World Precision | <<locked>> | 80% | 41,495 psi | 65% | 2867 fps | 99.3% |
| Shooters World SW4350 | <<locked>> | 90% | 44,382 psi | 70% | 2943 fps | 95.4% |
| SNPE Vectan SP 11 | <<locked>> | 80% | 37,710 psi | 59% | 2841 fps | 97.4% |
| SNPE Vectan SP 7 | <<locked>> | 80% | 47,108 psi | 74% | 2979 fps | 98% |
| SNPE Vectan SP 9 | <<locked>> | 80% | 45,034 psi | 71% | 2956 fps | 99% |
| SNPE Vectan Tubal 3000 | <<locked>> | 80% | 46,630 psi | 73% | 2887 fps | 100% |
| SNPE Vectan Tubal 5000 | <<locked>> | 80% | 38,870 psi | 61% | 2736 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 90% | 46,586 psi | 73% | 2920 fps | 95.8% |
| Somchem S321 | <<locked>> | 80% | 52,924 psi | 83% | 3087 fps | 100% |
| Somchem S335 | <<locked>> | 80% | 46,427 psi | 73% | 2890 fps | 100% |
| Somchem S341 | <<locked>> | 80% | 46,833 psi | 73% | 2976 fps | 99.2% |
| Somchem S355 | <<locked>> | 80% | 37,391 psi | 59% | 2795 fps | 97.8% |
| Somchem S365 | <<locked>> | 80% | 27,122 psi | 43% | 2595 fps | 95.1% |
| Somchem S385 | <<locked>> | 98% | 46,572 psi | 73% | 3012 fps | 95.1% |
| Vihtavuori N130 | <<locked>> | 80% | 52,591 psi | 82% | 2953 fps | 100% |
| Vihtavuori N133 | <<locked>> | 80% | 47,079 psi | 74% | 2881 fps | 100% |
| Vihtavuori N135 | <<locked>> | 80% | 42,757 psi | 67% | 2864 fps | 100% |
| Vihtavuori N140 | <<locked>> | 80% | 43,410 psi | 68% | 2874 fps | 100% |
| Vihtavuori N150 | <<locked>> | 80% | 35,491 psi | 56% | 2723 fps | 98.5% |
| Vihtavuori N160 | <<locked>> | 84% | 36,492 psi | 57% | 2789 fps | 95.5% |
| Vihtavuori N530 | <<locked>> | 80% | 48,805 psi | 76% | 2999 fps | 99.9% |
| Vihtavuori N540 | <<locked>> | 80% | 42,003 psi | 66% | 2861 fps | 100% |
| Vihtavuori N550 | <<locked>> | 84% | 35,824 psi | 56% | 2785 fps | 95% |
| Vihtavuori N555 | <<locked>> | 92% | 34,896 psi | 55% | 2828 fps | 95.9% |
| Winchester 6.5 StaBALL | <<locked>> | 80% | 31,517 psi | 49% | 2635 fps | 96% |
| Winchester 748 | <<locked>> | 80% | 48,892 psi | 77% | 3048 fps | 100% |
| Winchester 760 | <<locked>> | 90% | 45,759 psi | 72% | 3031 fps | 95.7% |
| Winchester StaBALL HD | <<locked>> | 94% | 30,255 psi | 47% | 2762 fps | 95.4% |
| Winchester StaBALL Match | <<locked>> | 80% | 44,686 psi | 70% | 2959 fps | 99.3% |
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 | Barnes TSX BT. Alliant Power Pro 2000-MR delivers the highest muzzle velocity at 3,304 fps; across all powders the maximum-charge window runs from 1,965 fps to 3,304 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 60, ReloadSwiss RS 70, Hodgdon Superformance rank at the top here: for .255 GS with the .257 | 100gr | Barnes TSX BT 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.