Load Specifications
Bullet Manufacturer:Speer
Bullet Weight:120 gr
Bullet Diameter:0.257"
Bullet Length:<<locked>>
Caliber:.255 GS load data
Case Length (l3):2.165"
Cartridge Length (C.O.L.):<<locked>>
Case Capacity:62 Grains of Water
Primer Size:Large Rifle (LR)
Barrel Length:24"
Max. allowed Pressure:63,817 psi
Recommended Twist Rate:1:10.5
Load data in caliber .255 GS with .257 | 120gr | Speer Boat-Tail bullet and 101 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-26 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 2495 | <<locked>> | 82% | 54,810 psi | 86% | 2795 fps | 100% |
| Accurate 2700 | <<locked>> | 84% | 55,854 psi | 88% | 2864 fps | 98.7% |
| Accurate 3100ᴾ | <<locked>> | 100% | 53,679 psi | 84% | 2907 fps | 99.5% |
| Accurate 4064 | <<locked>> | 84% | 55,216 psi | 87% | 2851 fps | 100% |
| Accurate 4350 | <<locked>> | 92% | 55,985 psi | 88% | 2963 fps | 100% |
| Accurate MAGPROᴾ | <<locked>> | 100% | 55,970 psi | 88% | 3051 fps | 96.1% |
| ADI AR 2206H | <<locked>> | 82% | 57,450 psi | 90% | 2927 fps | 100% |
| ADI AR 2208 | <<locked>> | 86% | 55,332 psi | 87% | 2887 fps | 100% |
| ADI AR 2209 | <<locked>> | 98% | 56,898 psi | 89% | 3002 fps | 98.3% |
| ADI AR 2213ᴾ | <<locked>> | 100% | 54,636 psi | 86% | 2995 fps | 96.8% |
| Alliant Power Pro 2000-MR | <<locked>> | 82% | 54,505 psi | 85% | 3005 fps | 100% |
| Alliant Power Pro Varmint | <<locked>> | 98% | 57,000 psi | 89% | 2999 fps | 98.4% |
| Alliant Reloder- TS 15.5 | <<locked>> | 86% | 56,173 psi | 88% | 2910 fps | 100% |
| Alliant Reloder-15 | <<locked>> | 84% | 56,449 psi | 88% | 2933 fps | 100% |
| Alliant Reloder-16 | <<locked>> | 94% | 56,768 psi | 89% | 3018 fps | 100% |
| Alliant Reloder-17 | <<locked>> | 88% | 54,056 psi | 85% | 2986 fps | 100% |
| Alliant Reloder-19 | <<locked>> | 98% | 56,246 psi | 88% | 2992 fps | 98.3% |
| Alliant Reloder-22ᴾ | <<locked>> | 100% | 53,461 psi | 84% | 2992 fps | 98% |
| Alliant Reloder-23ᴾ | <<locked>> | 100% | 50,415 psi | 79% | 2923 fps | 100% |
| Alliant Reloder-25ᴾ | <<locked>> | 100% | 43,830 psi | 69% | 2844 fps | 99% |
| Alliant Reloder-26 | <<locked>> | 98% | 54,085 psi | 85% | 3064 fps | 100% |
| Baschieri & Pellagri 107 | <<locked>> | 82% | 57,508 psi | 90% | 2949 fps | 100% |
| Bofors RP15ᴾ | <<locked>> | 100% | 49,052 psi | 77% | 2913 fps | 97% |
| Bofors RP3 | <<locked>> | 86% | 57,101 psi | 89% | 2927 fps | 100% |
| Bofors RP5ᴾ | <<locked>> | 100% | 53,461 psi | 84% | 2992 fps | 98% |
| Bofors RP7 | <<locked>> | 90% | 56,318 psi | 88% | 2910 fps | 98.9% |
| Hodgdon H380 | <<locked>> | 86% | 57,522 psi | 90% | 2946 fps | 100% |
| Hodgdon H414 | <<locked>> | 90% | 54,578 psi | 86% | 2959 fps | 99.2% |
| Hodgdon H4350 | <<locked>> | 88% | 54,259 psi | 85% | 2913 fps | 98.2% |
| Hodgdon H4831 | <<locked>> | 98% | 54,824 psi | 86% | 2940 fps | 96.1% |
| Hodgdon H4831 SCᴾ | <<locked>> | 100% | 57,392 psi | 90% | 2979 fps | 96.7% |
| Hodgdon Hybrid 100V | <<locked>> | 96% | 56,840 psi | 89% | 2936 fps | 100% |
| Hodgdon LEVERevolution | <<locked>> | 82% | 54,897 psi | 86% | 2923 fps | 100% |
| Hodgdon Superformance | <<locked>> | 90% | 54,563 psi | 86% | 2992 fps | 99% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 36,405 psi | 57% | 1811 fps | 100% |
| Hodgdon VARGET | <<locked>> | 82% | 55,738 psi | 87% | 2887 fps | 100% |
| IMR 4064 | <<locked>> | 84% | 54,795 psi | 86% | 2867 fps | 100% |
| IMR 4166 Enduron | <<locked>> | 84% | 57,450 psi | 90% | 2904 fps | 99.4% |
| IMR 4350 | <<locked>> | 94% | 57,406 psi | 90% | 2943 fps | 99.1% |
| IMR 4451 Enduron | <<locked>> | 88% | 54,578 psi | 86% | 2884 fps | 99% |
| IMR 4831 | <<locked>> | 94% | 56,304 psi | 88% | 2949 fps | 100% |
| IMR 4895 | <<locked>> | 82% | 54,143 psi | 85% | 2904 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 98% | 56,304 psi | 88% | 2927 fps | 96.6% |
| IMR 7828 SSCᴾ | <<locked>> | 100% | 51,822 psi | 81% | 2963 fps | 96.3% |
| Lovex S060 | <<locked>> | 82% | 56,318 psi | 88% | 2854 fps | 100% |
| Lovex S062 | <<locked>> | 84% | 55,042 psi | 86% | 2861 fps | 100% |
| Lovex S065 | <<locked>> | 90% | 54,418 psi | 85% | 2877 fps | 99.7% |
| Lovex S070 | <<locked>> | 92% | 55,985 psi | 88% | 2923 fps | 99.4% |
| Lovex S071ᴾ | <<locked>> | 100% | 44,614 psi | 70% | 2753 fps | 98.3% |
| Norma 201 | <<locked>> | 82% | 56,231 psi | 88% | 2871 fps | 100% |
| Norma 202 | <<locked>> | 82% | 56,840 psi | 89% | 2864 fps | 100% |
| Norma 203B | <<locked>> | 84% | 55,738 psi | 87% | 2917 fps | 100% |
| Norma 204 | <<locked>> | 92% | 54,302 psi | 85% | 2936 fps | 97.8% |
| Norma MRPᴾ | <<locked>> | 100% | 56,971 psi | 89% | 3081 fps | 99.5% |
| Norma URP | <<locked>> | 92% | 54,679 psi | 86% | 2946 fps | 100% |
| Ramshot Big Game | <<locked>> | 84% | 56,449 psi | 88% | 2943 fps | 100% |
| Ramshot Grandᴾ | <<locked>> | 100% | 52,214 psi | 82% | 2976 fps | 96.7% |
| Ramshot Hunter | <<locked>> | 94% | 57,000 psi | 89% | 2999 fps | 99.8% |
| Ramshot Magnumᴾ | <<locked>> | 100% | 46,702 psi | 73% | 2851 fps | 97.2% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 36,970 psi | 58% | 1850 fps | 100% |
| ReloadSwiss RS 50 | <<locked>> | 86% | 57,377 psi | 90% | 2927 fps | 99.6% |
| ReloadSwiss RS 52 | <<locked>> | 82% | 57,392 psi | 90% | 3002 fps | 100% |
| ReloadSwiss RS 60 | <<locked>> | 88% | 57,450 psi | 90% | 3031 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 92% | 55,941 psi | 88% | 2986 fps | 100% |
| ReloadSwiss RS 70 | <<locked>> | 92% | 54,302 psi | 85% | 3009 fps | 100% |
| ReloadSwiss RS 76ᴾ | <<locked>> | 100% | 42,801 psi | 67% | 2861 fps | 97.1% |
| Rottweil R 902 | <<locked>> | 84% | 56,927 psi | 89% | 2871 fps | 100% |
| Rottweil R 903 | <<locked>> | 88% | 56,956 psi | 89% | 2920 fps | 100% |
| Rottweil R 904 | <<locked>> | 96% | 55,201 psi | 87% | 2920 fps | 97% |
| Rottweil R 905 | <<locked>> | 98% | 55,390 psi | 87% | 2976 fps | 98.3% |
| Rottweil R 907 | <<locked>> | 90% | 56,318 psi | 88% | 2910 fps | 98.9% |
| Shooters World Long Rifle | <<locked>> | 90% | 54,418 psi | 85% | 2877 fps | 99.7% |
| Shooters World Precision | <<locked>> | 84% | 55,042 psi | 86% | 2861 fps | 100% |
| Shooters World SW4350 | <<locked>> | 92% | 55,985 psi | 88% | 2923 fps | 99.4% |
| SNPE Vectan SP 11 | <<locked>> | 86% | 54,868 psi | 86% | 2927 fps | 100% |
| SNPE Vectan SP 3 | <<locked>> | 82% | 57,421 psi | 90% | 2779 fps | 100% |
| SNPE Vectan SP 9 | <<locked>> | 82% | 55,999 psi | 88% | 2900 fps | 100% |
| SNPE Vectan Tubal 3000 | <<locked>> | 82% | 56,927 psi | 89% | 2799 fps | 100% |
| SNPE Vectan Tubal 5000 | <<locked>> | 86% | 54,621 psi | 86% | 2756 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 90% | 54,360 psi | 85% | 2835 fps | 99.1% |
| SNPE Vectan Tubal 8000 | <<locked>> | 98% | 54,911 psi | 86% | 2969 fps | 98.2% |
| Somchem S335 | <<locked>> | 82% | 56,695 psi | 89% | 2795 fps | 100% |
| Somchem S355 | <<locked>> | 88% | 56,797 psi | 89% | 2913 fps | 100% |
| Somchem S361 | <<locked>> | 96% | 56,927 psi | 89% | 2910 fps | 96.5% |
| Somchem S365 | <<locked>> | 96% | 57,653 psi | 90% | 2999 fps | 100% |
| Somchem S385 | <<locked>> | 98% | 55,970 psi | 88% | 2949 fps | 98.9% |
| Vihtavuori N133 | <<locked>> | 82% | 57,421 psi | 90% | 2779 fps | 100% |
| Vihtavuori N135 | <<locked>> | 84% | 57,305 psi | 90% | 2828 fps | 100% |
| Vihtavuori N140 | <<locked>> | 84% | 57,609 psi | 90% | 2848 fps | 100% |
| Vihtavuori N150 | <<locked>> | 88% | 54,650 psi | 86% | 2838 fps | 100% |
| Vihtavuori N160 | <<locked>> | 92% | 56,797 psi | 89% | 2940 fps | 100% |
| Vihtavuori N165ᴾ | <<locked>> | 100% | 51,706 psi | 81% | 2867 fps | 98% |
| Vihtavuori N540 | <<locked>> | 84% | 55,738 psi | 87% | 2844 fps | 100% |
| Vihtavuori N550 | <<locked>> | 92% | 55,782 psi | 87% | 2943 fps | 100% |
| Vihtavuori N555ᴾ | <<locked>> | 100% | 56,420 psi | 88% | 3005 fps | 100% |
| Vihtavuori N560ᴾ | <<locked>> | 100% | 57,232 psi | 90% | 3071 fps | 97% |
| Winchester 6.5 StaBALL | <<locked>> | 92% | 56,463 psi | 88% | 2904 fps | 100% |
| Winchester 760 | <<locked>> | 90% | 54,578 psi | 86% | 2959 fps | 99.2% |
| Winchester StaBALL HDᴾ | <<locked>> | 100% | 45,556 psi | 71% | 2982 fps | 100% |
| Winchester StaBALL Match | <<locked>> | 82% | 56,101 psi | 88% | 2907 fps | 100% |
| Winchester Supreme 780ᴾ | <<locked>> | 100% | 56,347 psi | 88% | 2946 fps | 98.2% |
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 2495 | <<locked>> | 80% | 51,430 psi | 81% | 2749 fps | 100% |
| Accurate 2700 | <<locked>> | 80% | 49,168 psi | 77% | 2753 fps | 97.7% |
| Accurate 3100 | <<locked>> | 86% | 33,388 psi | 52% | 2513 fps | 95% |
| Accurate 4064 | <<locked>> | 80% | 48,733 psi | 76% | 2756 fps | 100% |
| Accurate 4350 | <<locked>> | 80% | 37,086 psi | 58% | 2615 fps | 98% |
| Accurate MAGPRO | <<locked>> | 98% | 52,083 psi | 82% | 2986 fps | 95.2% |
| ADI AR 2206H | <<locked>> | 80% | 54,085 psi | 85% | 2877 fps | 100% |
| ADI AR 2208 | <<locked>> | 80% | 45,977 psi | 72% | 2730 fps | 99.7% |
| ADI AR 2209 | <<locked>> | 90% | 43,830 psi | 69% | 2766 fps | 95.4% |
| ADI AR 2213 | <<locked>> | 96% | 47,718 psi | 75% | 2867 fps | 95% |
| Alliant Power Pro 2000-MR | <<locked>> | 80% | 50,763 psi | 80% | 2946 fps | 100% |
| Alliant Power Pro Varmint | <<locked>> | 90% | 44,077 psi | 69% | 2772 fps | 95.6% |
| Alliant Reloder- TS 15.5 | <<locked>> | 80% | 46,383 psi | 73% | 2753 fps | 100% |
| Alliant Reloder-15 | <<locked>> | 80% | 49,617 psi | 78% | 2822 fps | 100% |
| Alliant Reloder-16 | <<locked>> | 80% | 36,129 psi | 57% | 2625 fps | 98.1% |
| Alliant Reloder-17 | <<locked>> | 80% | 40,901 psi | 64% | 2753 fps | 99.9% |
| Alliant Reloder-19 | <<locked>> | 90% | 43,555 psi | 68% | 2762 fps | 95.5% |
| Alliant Reloder-22 | <<locked>> | 94% | 43,540 psi | 68% | 2808 fps | 95.7% |
| Alliant Reloder-23 | <<locked>> | 80% | 26,527 psi | 42% | 2375 fps | 95.6% |
| Alliant Reloder-25 | <<locked>> | 92% | 33,997 psi | 53% | 2605 fps | 95.7% |
| Alliant Reloder-26 | 46.6 gr | 84% | 32,430 psi | 51% | 2608 fps | 96% |
| Baschieri & Pellagri 107 | <<locked>> | 80% | 53,795 psi | 84% | 2890 fps | 100% |
| Bofors RP15 | <<locked>> | 96% | 42,946 psi | 67% | 2792 fps | 95.3% |
| Bofors RP3 | <<locked>> | 80% | 46,615 psi | 73% | 2762 fps | 100% |
| Bofors RP5 | <<locked>> | 94% | 43,540 psi | 68% | 2808 fps | 95.7% |
| Bofors RP7 | <<locked>> | 80% | 41,089 psi | 64% | 2631 fps | 95.9% |
| Hodgdon H380 | <<locked>> | 80% | 47,123 psi | 74% | 2776 fps | 99.4% |
| Hodgdon H414 | <<locked>> | 80% | 39,102 psi | 61% | 2664 fps | 95.9% |
| Hodgdon H4350 | <<locked>> | 80% | 41,887 psi | 66% | 2680 fps | 95.3% |
| Hodgdon H4831 | <<locked>> | 96% | 51,068 psi | 80% | 2877 fps | 95.2% |
| Hodgdon H4831 SC | <<locked>> | 96% | 50,096 psi | 79% | 2861 fps | 95% |
| Hodgdon Hybrid 100V | <<locked>> | 80% | 33,605 psi | 53% | 2516 fps | 98.6% |
| Hodgdon LEVERevolution | <<locked>> | 80% | 51,271 psi | 80% | 2867 fps | 100% |
| Hodgdon Superformance | 45.8 gr | 80% | 38,043 psi | 60% | 2671 fps | 95% |
| Hodgdon TrailBoss | <<locked>> | 80% | 27,151 psi | 43% | 1617 fps | 100% |
| Hodgdon VARGET | <<locked>> | 80% | 52,388 psi | 82% | 2838 fps | 100% |
| IMR 4064 | <<locked>> | 80% | 48,370 psi | 76% | 2762 fps | 99.9% |
| IMR 4166 Enduron | <<locked>> | 80% | 50,589 psi | 79% | 2792 fps | 98.5% |
| IMR 4350 | <<locked>> | 82% | 39,262 psi | 62% | 2612 fps | 95.3% |
| IMR 4451 Enduron | <<locked>> | 80% | 42,583 psi | 67% | 2664 fps | 96.8% |
| IMR 4831 | <<locked>> | 80% | 35,607 psi | 56% | 2566 fps | 97.7% |
| IMR 4895 | <<locked>> | 80% | 50,879 psi | 80% | 2851 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 94% | 49,864 psi | 78% | 2818 fps | 95.2% |
| IMR 7828 SSC | <<locked>> | 98% | 48,573 psi | 76% | 2900 fps | 95.4% |
| Lovex S060 | <<locked>> | 80% | 53,055 psi | 83% | 2802 fps | 100% |
| Lovex S062 | <<locked>> | 80% | 48,660 psi | 76% | 2762 fps | 100% |
| Lovex S065 | <<locked>> | 80% | 40,132 psi | 63% | 2615 fps | 97.5% |
| Lovex S070 | <<locked>> | 80% | 38,247 psi | 60% | 2592 fps | 95.9% |
| Lovex S071 | <<locked>> | 92% | 34,505 psi | 54% | 2539 fps | 95.5% |
| Norma 201 | <<locked>> | 80% | 52,881 psi | 83% | 2822 fps | 100% |
| Norma 202 | <<locked>> | 80% | 53,461 psi | 84% | 2815 fps | 100% |
| Norma 203B | <<locked>> | 80% | 48,965 psi | 77% | 2808 fps | 100% |
| Norma 204 | <<locked>> | 86% | 44,309 psi | 69% | 2756 fps | 95.5% |
| Norma MRP | <<locked>> | 88% | 37,478 psi | 59% | 2703 fps | 95.1% |
| Norma URP | <<locked>> | 80% | 36,796 psi | 58% | 2608 fps | 97.8% |
| Ramshot Big Game | <<locked>> | 80% | 49,298 psi | 77% | 2831 fps | 100% |
| Ramshot Grand | <<locked>> | 98% | 48,501 psi | 76% | 2910 fps | 95.7% |
| Ramshot Hunter | <<locked>> | 80% | 35,665 psi | 56% | 2592 fps | 95.7% |
| Ramshot Magnum | <<locked>> | 96% | 40,306 psi | 63% | 2720 fps | 95.3% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 27,731 psi | 43% | 1657 fps | 100% |
| ReloadSwiss RS 50 | <<locked>> | 80% | 47,268 psi | 74% | 2762 fps | 98.5% |
| ReloadSwiss RS 52 | <<locked>> | 80% | 53,505 psi | 84% | 2943 fps | 100% |
| ReloadSwiss RS 60 | <<locked>> | 80% | 43,497 psi | 68% | 2808 fps | 100% |
| ReloadSwiss RS 62 | <<locked>> | 80% | 36,840 psi | 58% | 2635 fps | 97.6% |
| ReloadSwiss RS 70 | 44 gr | 80% | 35,810 psi | 56% | 2638 fps | 96.9% |
| ReloadSwiss RS 76 | <<locked>> | 98% | 39,914 psi | 63% | 2789 fps | 96% |
| Rottweil R 902 | <<locked>> | 80% | 50,343 psi | 79% | 2772 fps | 100% |
| Rottweil R 903 | <<locked>> | 80% | 43,888 psi | 69% | 2707 fps | 100% |
| Rottweil R 904 | <<locked>> | 92% | 48,385 psi | 76% | 2802 fps | 95.5% |
| Rottweil R 905 | <<locked>> | 90% | 42,482 psi | 67% | 2743 fps | 95.4% |
| Rottweil R 907 | <<locked>> | 80% | 41,089 psi | 64% | 2631 fps | 95.9% |
| Shooters World Long Rifle | <<locked>> | 80% | 40,132 psi | 63% | 2615 fps | 97.5% |
| Shooters World Precision | <<locked>> | 80% | 48,660 psi | 76% | 2762 fps | 100% |
| Shooters World SW4350 | <<locked>> | 80% | 38,247 psi | 60% | 2592 fps | 95.9% |
| SNPE Vectan SP 11 | <<locked>> | 80% | 44,991 psi | 71% | 2762 fps | 99.9% |
| SNPE Vectan SP 3 | <<locked>> | 80% | 53,998 psi | 85% | 2733 fps | 100% |
| SNPE Vectan SP 9 | <<locked>> | 80% | 52,402 psi | 82% | 2844 fps | 100% |
| SNPE Vectan Tubal 3000 | <<locked>> | 80% | 53,476 psi | 84% | 2749 fps | 100% |
| SNPE Vectan Tubal 5000 | <<locked>> | 80% | 45,179 psi | 71% | 2618 fps | 100% |
| SNPE Vectan Tubal 7000 | <<locked>> | 80% | 39,320 psi | 62% | 2559 fps | 96.1% |
| SNPE Vectan Tubal 8000 | <<locked>> | 90% | 42,090 psi | 66% | 2736 fps | 95.2% |
| Somchem S335 | <<locked>> | 80% | 53,432 psi | 84% | 2749 fps | 100% |
| Somchem S355 | <<locked>> | 80% | 44,353 psi | 70% | 2710 fps | 99.9% |
| Somchem S361 | <<locked>> | 94% | 53,243 psi | 83% | 2854 fps | 95.8% |
| Somchem S365 | <<locked>> | 80% | 33,417 psi | 52% | 2569 fps | 99.5% |
| Somchem S385 | <<locked>> | 88% | 40,393 psi | 63% | 2667 fps | 95.7% |
| Vihtavuori N133 | <<locked>> | 80% | 53,998 psi | 85% | 2733 fps | 100% |
| Vihtavuori N135 | <<locked>> | 80% | 50,430 psi | 79% | 2733 fps | 100% |
| Vihtavuori N140 | <<locked>> | 80% | 50,662 psi | 79% | 2746 fps | 100% |
| Vihtavuori N150 | <<locked>> | 80% | 42,192 psi | 66% | 2638 fps | 100% |
| Vihtavuori N160 | <<locked>> | 80% | 38,290 psi | 60% | 2612 fps | 98.2% |
| Vihtavuori N165 | <<locked>> | 92% | 39,769 psi | 62% | 2644 fps | 95% |
| Vihtavuori N540 | <<locked>> | 80% | 49,124 psi | 77% | 2743 fps | 100% |
| Vihtavuori N550 | <<locked>> | 80% | 37,797 psi | 59% | 2612 fps | 97.9% |
| Vihtavuori N555 | <<locked>> | 80% | 29,167 psi | 46% | 2454 fps | 95.8% |
| Vihtavuori N560 | <<locked>> | 96% | 49,777 psi | 78% | 2940 fps | 95.3% |
| Winchester 6.5 StaBALL | <<locked>> | 80% | 37,362 psi | 59% | 2579 fps | 99.5% |
| Winchester 760 | <<locked>> | 80% | 39,102 psi | 61% | 2664 fps | 95.9% |
| Winchester StaBALL HD | <<locked>> | 82% | 24,976 psi | 39% | 2395 fps | 95% |
| Winchester StaBALL Match | <<locked>> | 80% | 52,446 psi | 82% | 2854 fps | 100% |
| Winchester Supreme 780 | <<locked>> | 92% | 42,685 psi | 67% | 2710 fps | 95.2% |
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 101 powders for .255 GS loaded with the .257 | 120gr | Speer Boat-Tail. Norma MRP delivers the highest muzzle velocity at 3,081 fps; across all powders the maximum-charge window runs from 1,811 fps to 3,081 fps. Accurate 3100 gives the best case fill at 100 %, and 101 of the 101 powders fall inside the usable 80–100 % fill window.
Relative to the caliber's maximum pressure (440 MPa), the top charges use 57–90 %, leaving at least 10 % headroom. The 120.0 gr projectile in 0.257" calls for a 1:10.5 twist; slower twists will usually not stabilise this weight. Accurate 3100, Accurate MAGPRO, ADI AR 2213 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-26, Hodgdon Superformance rank at the top here: for .255 GS with the .257 | 120gr | Speer Boat-Tail 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.