Load Specifications
Load data in caliber .255 GS with .257 | 100gr | Frontier BTSP bullet and 96 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>> | 82% | 54,592 psi | 86% | 3015 fps | 100% |
| Accurate 2495 | <<locked>> | 88% | 57,392 psi | 90% | 3091 fps | 100% |
| Accurate 2520 | <<locked>> | 82% | 55,187 psi | 86% | 3107 fps | 100% |
| Accurate 2700 | <<locked>> | 88% | 55,941 psi | 88% | 3084 fps | 96.9% |
| Accurate 3100ᴾ | <<locked>> | 100% | 44,556 psi | 70% | 2969 fps | 96.3% |
| Accurate 4064 | <<locked>> | 90% | 57,363 psi | 90% | 3140 fps | 100% |
| Accurate 4350 | <<locked>> | 98% | 57,493 psi | 90% | 3228 fps | 99.7% |
| ADI AR 2206H | <<locked>> | 86% | 57,087 psi | 89% | 3169 fps | 100% |
| ADI AR 2208 | <<locked>> | 90% | 54,752 psi | 86% | 3117 fps | 99.7% |
| ADI Benchmark 8208 | <<locked>> | 84% | 55,985 psi | 88% | 3117 fps | 100% |
| Alliant AR-Comp | <<locked>> | 84% | 57,217 psi | 90% | 3091 fps | 100% |
| Alliant Power Pro 2000-MR | <<locked>> | 88% | 57,406 psi | 90% | 3304 fps | 99.9% |
| Alliant Reloder- TS 15.5 | <<locked>> | 90% | 54,984 psi | 86% | 3140 fps | 100% |
| Alliant Reloder-15 | <<locked>> | 88% | 55,347 psi | 87% | 3163 fps | 99.8% |
| Alliant Reloder-16 | <<locked>> | 98% | 54,665 psi | 86% | 3228 fps | 99.7% |
| Alliant Reloder-17 | <<locked>> | 94% | 56,391 psi | 88% | 3274 fps | 100% |
| Alliant Reloder-23ᴾ | <<locked>> | 100% | 42,177 psi | 66% | 2999 fps | 99% |
| Alliant Reloder-26ᴾ | <<locked>> | 100% | 47,601 psi | 75% | 3182 fps | 98.5% |
| Baschieri & Pellagri 107 | <<locked>> | 86% | 57,363 psi | 90% | 3189 fps | 99.7% |
| Bofors RP3 | <<locked>> | 90% | 55,927 psi | 88% | 3159 fps | 100% |
| Bofors RP7 | <<locked>> | 94% | 55,550 psi | 87% | 3120 fps | 97.1% |
| Hodgdon Benchmark | <<locked>> | 84% | 57,363 psi | 90% | 3097 fps | 100% |
| Hodgdon BL-C2 | <<locked>> | 84% | 55,738 psi | 87% | 3146 fps | 100% |
| Hodgdon H380 | <<locked>> | 90% | 56,782 psi | 89% | 3173 fps | 99.4% |
| Hodgdon H414 | <<locked>> | 96% | 56,521 psi | 89% | 3225 fps | 98% |
| Hodgdon H4350 | <<locked>> | 94% | 56,811 psi | 89% | 3182 fps | 96.7% |
| Hodgdon H4895 | <<locked>> | 86% | 57,696 psi | 90% | 3182 fps | 100% |
| Hodgdon Hybrid 100Vᴾ | <<locked>> | 100% | 54,766 psi | 86% | 3153 fps | 100% |
| Hodgdon LEVERevolution | <<locked>> | 88% | 57,479 psi | 90% | 3215 fps | 100% |
| Hodgdon Superformance | <<locked>> | 96% | 57,580 psi | 90% | 3268 fps | 97.8% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 35,650 psi | 56% | 1959 fps | 100% |
| Hodgdon VARGET | <<locked>> | 86% | 55,492 psi | 87% | 3130 fps | 100% |
| IMR 3031 | <<locked>> | 84% | 54,491 psi | 85% | 3114 fps | 100% |
| IMR 4064 | <<locked>> | 90% | 57,667 psi | 90% | 3153 fps | 99.9% |
| IMR 4166 Enduron | <<locked>> | 88% | 57,566 psi | 90% | 3133 fps | 98% |
| IMR 4350 | <<locked>> | 98% | 56,202 psi | 88% | 3150 fps | 97.3% |
| IMR 4451 Enduron | <<locked>> | 94% | 57,363 psi | 90% | 3153 fps | 97.9% |
| IMR 4831 | <<locked>> | 98% | 54,288 psi | 85% | 3159 fps | 99.5% |
| IMR 4895 | <<locked>> | 88% | 56,782 psi | 89% | 3196 fps | 100% |
| IMR 8208 XBR | <<locked>> | 84% | 55,985 psi | 88% | 3117 fps | 100% |
| Lovex D073.6 | <<locked>> | 86% | 57,479 psi | 90% | 3146 fps | 100% |
| Lovex S060 | <<locked>> | 86% | 56,275 psi | 88% | 3091 fps | 99.9% |
| Lovex S062 | <<locked>> | 90% | 57,580 psi | 90% | 3146 fps | 100% |
| Lovex S065 | <<locked>> | 96% | 57,159 psi | 90% | 3153 fps | 98.9% |
| Lovex S070 | <<locked>> | 96% | 54,679 psi | 86% | 3130 fps | 97.7% |
| Norma 201 | <<locked>> | 86% | 55,956 psi | 88% | 3117 fps | 100% |
| Norma 202 | <<locked>> | 86% | 56,434 psi | 88% | 3114 fps | 100% |
| Norma 203B | <<locked>> | 88% | 54,563 psi | 86% | 3146 fps | 99.9% |
| Norma 204 | <<locked>> | 98% | 57,072 psi | 89% | 3202 fps | 96.2% |
| Norma URP | <<locked>> | 98% | 56,333 psi | 88% | 3215 fps | 99.6% |
| Ramshot Big Game | <<locked>> | 88% | 55,535 psi | 87% | 3176 fps | 99.9% |
| Ramshot Hunter | <<locked>> | 98% | 55,288 psi | 87% | 3209 fps | 98.5% |
| Ramshot TAC | <<locked>> | 84% | 56,507 psi | 89% | 3140 fps | 99% |
| Ramshot Wild Boar | <<locked>> | 84% | 55,985 psi | 88% | 3153 fps | 99.9% |
| Ramshot X-Terminator | <<locked>> | 82% | 56,811 psi | 89% | 3117 fps | 99.9% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 36,071 psi | 57% | 2005 fps | 100% |
| ReloadSwiss RS 50 | <<locked>> | 90% | 56,768 psi | 89% | 3150 fps | 98.4% |
| ReloadSwiss RS 52 | <<locked>> | 86% | 55,956 psi | 88% | 3232 fps | 99.8% |
| ReloadSwiss RS 60 | <<locked>> | 92% | 55,927 psi | 88% | 3271 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 98% | 57,334 psi | 90% | 3251 fps | 99.6% |
| ReloadSwiss RS 70 | <<locked>> | 98% | 56,710 psi | 89% | 3284 fps | 99.5% |
| Rottweil R 901 | <<locked>> | 84% | 56,855 psi | 89% | 3097 fps | 100% |
| Rottweil R 902 | <<locked>> | 88% | 56,289 psi | 88% | 3110 fps | 100% |
| Rottweil R 903 | <<locked>> | 92% | 55,796 psi | 87% | 3150 fps | 100% |
| Rottweil R 907 | <<locked>> | 94% | 55,550 psi | 87% | 3120 fps | 97.1% |
| Shooters World Long Rifle | <<locked>> | 96% | 57,159 psi | 90% | 3153 fps | 98.9% |
| Shooters World Match Rifle | <<locked>> | 86% | 57,479 psi | 90% | 3146 fps | 100% |
| Shooters World Precision | <<locked>> | 90% | 57,580 psi | 90% | 3146 fps | 100% |
| Shooters World SW4350 | <<locked>> | 96% | 54,679 psi | 86% | 3130 fps | 97.7% |
| SNPE Vectan SP 11 | <<locked>> | 92% | 57,406 psi | 90% | 3212 fps | 100% |
| SNPE Vectan SP 7 | <<locked>> | 84% | 54,839 psi | 86% | 3110 fps | 99.1% |
| SNPE Vectan SP 9 | <<locked>> | 86% | 55,448 psi | 87% | 3136 fps | 99.9% |
| SNPE Vectan Tubal 3000 | <<locked>> | 86% | 57,000 psi | 89% | 3045 fps | 100% |
| SNPE Vectan Tubal 5000 | <<locked>> | 92% | 57,493 psi | 90% | 3041 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 96% | 57,246 psi | 90% | 3097 fps | 97.9% |
| Somchem S321 | <<locked>> | 82% | 57,537 psi | 90% | 3153 fps | 100% |
| Somchem S335 | <<locked>> | 86% | 56,724 psi | 89% | 3045 fps | 100% |
| Somchem S341 | <<locked>> | 84% | 54,679 psi | 86% | 3104 fps | 99.9% |
| Somchem S355 | <<locked>> | 92% | 55,985 psi | 88% | 3146 fps | 100% |
| Somchem S365ᴾ | <<locked>> | 100% | 54,694 psi | 86% | 3219 fps | 100% |
| Somchem S385ᴾ | <<locked>> | 100% | 50,546 psi | 79% | 3081 fps | 96.1% |
| Vihtavuori N130 | <<locked>> | 82% | 56,666 psi | 89% | 3005 fps | 100% |
| Vihtavuori N133 | <<locked>> | 86% | 57,290 psi | 90% | 3028 fps | 100% |
| Vihtavuori N135 | <<locked>> | 88% | 56,289 psi | 88% | 3074 fps | 100% |
| Vihtavuori N140 | <<locked>> | 88% | 57,217 psi | 90% | 3091 fps | 100% |
| Vihtavuori N150 | <<locked>> | 94% | 57,435 psi | 90% | 3123 fps | 100% |
| Vihtavuori N160 | <<locked>> | 96% | 55,114 psi | 86% | 3153 fps | 99.4% |
| Vihtavuori N530 | <<locked>> | 84% | 56,637 psi | 89% | 3120 fps | 100% |
| Vihtavuori N540 | <<locked>> | 88% | 55,201 psi | 87% | 3084 fps | 100% |
| Vihtavuori N550 | <<locked>> | 96% | 54,317 psi | 85% | 3159 fps | 99.3% |
| Vihtavuori N555ᴾ | <<locked>> | 100% | 46,731 psi | 73% | 3087 fps | 99% |
| Winchester 6.5 StaBALL | <<locked>> | 96% | 55,593 psi | 87% | 3130 fps | 100% |
| Winchester 748 | <<locked>> | 84% | 56,782 psi | 89% | 3169 fps | 100% |
| Winchester 760 | <<locked>> | 96% | 56,927 psi | 89% | 3232 fps | 98% |
| Winchester StaBALL HDᴾ | <<locked>> | 100% | 37,739 psi | 59% | 3002 fps | 99% |
| Winchester StaBALL Match | <<locked>> | 86% | 55,651 psi | 87% | 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% | 51,213 psi | 80% | 2963 fps | 100% |
| Accurate 2495 | <<locked>> | 80% | 44,106 psi | 69% | 2881 fps | 100% |
| Accurate 2520 | <<locked>> | 80% | 51,474 psi | 81% | 3048 fps | 100% |
| Accurate 2700 | <<locked>> | 84% | 49,139 psi | 77% | 2966 fps | 95.4% |
| Accurate 3100 | <<locked>> | 98% | 41,307 psi | 65% | 2900 fps | 95.3% |
| Accurate 4064 | <<locked>> | 80% | 41,698 psi | 65% | 2874 fps | 100% |
| Accurate 4350 | <<locked>> | 84% | 35,360 psi | 55% | 2792 fps | 95.2% |
| ADI AR 2206H | <<locked>> | 80% | 47,384 psi | 74% | 3002 fps | 99.3% |
| ADI AR 2208 | <<locked>> | 80% | 40,248 psi | 63% | 2835 fps | 97.4% |
| ADI Benchmark 8208 | <<locked>> | 80% | 49,458 psi | 78% | 3009 fps | 99.9% |
| Alliant AR-Comp | <<locked>> | 80% | 50,038 psi | 78% | 2989 fps | 100% |
| Alliant Power Pro 2000-MR | <<locked>> | 80% | 43,221 psi | 68% | 3031 fps | 98.1% |
| Alliant Reloder- TS 15.5 | <<locked>> | 80% | 40,030 psi | 63% | 2854 fps | 98.7% |
| Alliant Reloder-15 | <<locked>> | 80% | 43,018 psi | 67% | 2927 fps | 98.2% |
| Alliant Reloder-16 | <<locked>> | 84% | 35,273 psi | 55% | 2805 fps | 95.3% |
| Alliant Reloder-17 | <<locked>> | 80% | 34,795 psi | 55% | 2822 fps | 97% |
| Alliant Reloder-23 | <<locked>> | 90% | 30,792 psi | 48% | 2697 fps | 95% |
| Alliant Reloder-26 | <<locked>> | 94% | 38,348 psi | 60% | 2966 fps | 95.8% |
| Baschieri & Pellagri 107 | <<locked>> | 80% | 46,818 psi | 73% | 3002 fps | 98.5% |
| Bofors RP3 | <<locked>> | 80% | 39,856 psi | 62% | 2861 fps | 98.8% |
| Bofors RP7 | <<locked>> | 90% | 49,037 psi | 77% | 3002 fps | 95.7% |
| Hodgdon Benchmark | <<locked>> | 80% | 50,807 psi | 80% | 2992 fps | 100% |
| Hodgdon BL-C2 | <<locked>> | 80% | 48,573 psi | 76% | 3028 fps | 100% |
| Hodgdon H380 | <<locked>> | 80% | 40,451 psi | 63% | 2861 fps | 96.4% |
| Hodgdon H414 | <<locked>> | 90% | 46,383 psi | 73% | 3038 fps | 95.8% |
| Hodgdon H4350 | <<locked>> | 90% | 50,140 psi | 79% | 3064 fps | 95.2% |
| Hodgdon H4895 | <<locked>> | 80% | 47,834 psi | 75% | 3012 fps | 99.6% |
| Hodgdon Hybrid 100V | <<locked>> | 82% | 30,400 psi | 48% | 2631 fps | 95.1% |
| Hodgdon LEVERevolution | <<locked>> | 80% | 43,990 psi | 69% | 2979 fps | 99.4% |
| Hodgdon Superformance | 51 gr | 90% | 46,238 psi | 72% | 3058 fps | 95.1% |
| Hodgdon TrailBoss | <<locked>> | 80% | 26,658 psi | 42% | 1755 fps | 100% |
| Hodgdon VARGET | <<locked>> | 80% | 45,672 psi | 72% | 2953 fps | 99.3% |
| IMR 3031 | <<locked>> | 80% | 47,732 psi | 75% | 3005 fps | 100% |
| IMR 4064 | <<locked>> | 80% | 42,279 psi | 66% | 2871 fps | 98.1% |
| IMR 4166 Enduron | <<locked>> | 80% | 44,744 psi | 70% | 2894 fps | 95.2% |
| IMR 4350 | <<locked>> | 92% | 46,354 psi | 73% | 2972 fps | 95% |
| IMR 4451 Enduron | <<locked>> | 86% | 44,904 psi | 70% | 2923 fps | 95.1% |
| IMR 4831 | <<locked>> | 86% | 36,463 psi | 57% | 2802 fps | 95.8% |
| IMR 4895 | <<locked>> | 80% | 44,077 psi | 69% | 2963 fps | 98.9% |
| IMR 8208 XBR | <<locked>> | 80% | 49,458 psi | 78% | 3009 fps | 99.9% |
| Lovex D073.6 | <<locked>> | 80% | 46,804 psi | 73% | 2976 fps | 100% |
| Lovex S060 | <<locked>> | 80% | 46,818 psi | 73% | 2927 fps | 99.2% |
| Lovex S062 | <<locked>> | 80% | 42,047 psi | 66% | 2871 fps | 99.3% |
| Lovex S065 | <<locked>> | 84% | 39,450 psi | 62% | 2808 fps | 95.1% |
| Lovex S070 | <<locked>> | 90% | 45,353 psi | 71% | 2956 fps | 95.6% |
| Norma 201 | <<locked>> | 80% | 46,383 psi | 73% | 2946 fps | 99.8% |
| Norma 202 | <<locked>> | 80% | 46,673 psi | 73% | 2953 fps | 100% |
| Norma 203B | <<locked>> | 80% | 42,380 psi | 66% | 2917 fps | 98.5% |
| Norma 204 | <<locked>> | 96% | 53,127 psi | 83% | 3136 fps | 95.3% |
| Norma URP | <<locked>> | 84% | 35,447 psi | 56% | 2789 fps | 95.1% |
| Ramshot Big Game | <<locked>> | 80% | 42,003 psi | 66% | 2923 fps | 98.3% |
| Ramshot Hunter | <<locked>> | 90% | 42,380 psi | 66% | 2959 fps | 95.5% |
| Ramshot TAC | <<locked>> | 80% | 49,487 psi | 78% | 3015 fps | 97.9% |
| Ramshot Wild Boar | <<locked>> | 80% | 49,226 psi | 77% | 3035 fps | 99.5% |
| Ramshot X-Terminator | <<locked>> | 80% | 53,171 psi | 83% | 3058 fps | 99.7% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 26,861 psi | 42% | 1795 fps | 100% |
| ReloadSwiss RS 50 | <<locked>> | 82% | 43,816 psi | 69% | 2907 fps | 95.6% |
| ReloadSwiss RS 52 | <<locked>> | 80% | 45,614 psi | 71% | 3045 fps | 98.6% |
| ReloadSwiss RS 60 | 42.9 gr | 80% | 36,999 psi | 58% | 2894 fps | 99.5% |
| ReloadSwiss RS 62 | <<locked>> | 86% | 37,623 psi | 59% | 2871 fps | 95.7% |
| ReloadSwiss RS 70 | 47.9 gr | 88% | 40,205 psi | 63% | 2946 fps | 95.9% |
| Rottweil R 901 | <<locked>> | 80% | 50,241 psi | 79% | 2992 fps | 100% |
| Rottweil R 902 | <<locked>> | 80% | 44,077 psi | 69% | 2894 fps | 99.5% |
| Rottweil R 903 | <<locked>> | 80% | 37,449 psi | 59% | 2799 fps | 98% |
| Rottweil R 907 | <<locked>> | 90% | 49,037 psi | 77% | 3002 fps | 95.7% |
| Shooters World Long Rifle | <<locked>> | 84% | 39,450 psi | 62% | 2808 fps | 95.1% |
| Shooters World Match Rifle | <<locked>> | 80% | 46,804 psi | 73% | 2976 fps | 100% |
| Shooters World Precision | <<locked>> | 80% | 42,047 psi | 66% | 2871 fps | 99.3% |
| Shooters World SW4350 | <<locked>> | 90% | 45,353 psi | 71% | 2956 fps | 95.6% |
| SNPE Vectan SP 11 | <<locked>> | 80% | 38,493 psi | 60% | 2851 fps | 97.5% |
| SNPE Vectan SP 7 | <<locked>> | 80% | 47,761 psi | 75% | 2986 fps | 98% |
| SNPE Vectan SP 9 | <<locked>> | 80% | 45,788 psi | 72% | 2963 fps | 99.1% |
| SNPE Vectan Tubal 3000 | <<locked>> | 80% | 47,282 psi | 74% | 2890 fps | 100% |
| SNPE Vectan Tubal 5000 | <<locked>> | 80% | 39,566 psi | 62% | 2743 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 88% | 44,034 psi | 69% | 2861 fps | 95% |
| Somchem S321 | <<locked>> | 80% | 53,795 psi | 84% | 3094 fps | 100% |
| Somchem S335 | <<locked>> | 80% | 47,224 psi | 74% | 2894 fps | 100% |
| Somchem S341 | <<locked>> | 80% | 47,630 psi | 75% | 2982 fps | 99.3% |
| Somchem S355 | <<locked>> | 80% | 38,290 psi | 60% | 2808 fps | 98% |
| Somchem S365 | <<locked>> | 80% | 27,833 psi | 44% | 2612 fps | 95.4% |
| Somchem S385 | <<locked>> | 98% | 47,369 psi | 74% | 3022 fps | 95.3% |
| Vihtavuori N130 | <<locked>> | 80% | 53,229 psi | 83% | 2956 fps | 100% |
| Vihtavuori N133 | <<locked>> | 80% | 47,688 psi | 75% | 2884 fps | 100% |
| Vihtavuori N135 | <<locked>> | 80% | 43,598 psi | 68% | 2871 fps | 100% |
| Vihtavuori N140 | <<locked>> | 80% | 44,164 psi | 69% | 2881 fps | 100% |
| Vihtavuori N150 | <<locked>> | 80% | 36,347 psi | 57% | 2733 fps | 98.7% |
| Vihtavuori N160 | <<locked>> | 84% | 37,072 psi | 58% | 2795 fps | 95.7% |
| Vihtavuori N530 | <<locked>> | 80% | 49,559 psi | 78% | 3002 fps | 99.9% |
| Vihtavuori N540 | <<locked>> | 80% | 42,554 psi | 67% | 2864 fps | 100% |
| Vihtavuori N550 | <<locked>> | 84% | 36,506 psi | 57% | 2795 fps | 95.2% |
| Vihtavuori N555 | <<locked>> | 90% | 33,402 psi | 52% | 2782 fps | 95.2% |
| Winchester 6.5 StaBALL | <<locked>> | 80% | 32,285 psi | 51% | 2651 fps | 96.3% |
| Winchester 748 | <<locked>> | 80% | 49,676 psi | 78% | 3054 fps | 100% |
| Winchester 760 | <<locked>> | 90% | 46,383 psi | 73% | 3038 fps | 95.8% |
| Winchester StaBALL HD | <<locked>> | 94% | 31,082 psi | 49% | 2785 fps | 95.8% |
| Winchester StaBALL Match | <<locked>> | 80% | 45,498 psi | 71% | 2969 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 96 powders for .255 GS loaded with the .257 | 100gr | Frontier BTSP. Alliant Power Pro 2000-MR delivers the highest muzzle velocity at 3,304 fps; across all powders the maximum-charge window runs from 1,959 fps to 3,304 fps. Accurate 3100 gives the best case fill at 100 %, and 96 of the 96 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 1:9.0 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 | Frontier BTSP 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.