Load Specifications
Load data in caliber .338-378 Weath. Mag. with .338 | 250gr | Speer Grand Slam bullet and 52 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are Vihtavuori N570, Alliant Reloder-33 and Hodgdon Retumbo.
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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Max Load - Barrel Length: 26"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| Accurate 3100 | <<locked>> | 86% | 54,520 psi | 85% | 2772 fps | 100% |
| Accurate 8700ᴾ | <<locked>> | 100% | 45,179 psi | 71% | 2730 fps | 96.1% |
| Accurate MAGPRO | <<locked>> | 86% | 57,203 psi | 90% | 2936 fps | 99.8% |
| ADI AR 2209 | <<locked>> | 84% | 55,579 psi | 87% | 2854 fps | 100% |
| ADI AR 2213 | <<locked>> | 86% | 54,114 psi | 85% | 2874 fps | 99.9% |
| ADI AR 2217 | <<locked>> | 96% | 56,739 psi | 89% | 2910 fps | 100% |
| ADI AR 2218ᴾ | <<locked>> | 100% | 57,058 psi | 89% | 3035 fps | 99.3% |
| ADI AR 2225 | <<locked>> | 98% | 55,666 psi | 87% | 2933 fps | 100% |
| Alliant Reloder-19 | <<locked>> | 84% | 55,332 psi | 87% | 2844 fps | 100% |
| Alliant Reloder-22 | <<locked>> | 86% | 54,636 psi | 86% | 2867 fps | 100% |
| Alliant Reloder-23 | <<locked>> | 88% | 56,536 psi | 89% | 2825 fps | 100% |
| Alliant Reloder-25 | <<locked>> | 92% | 56,797 psi | 89% | 2900 fps | 100% |
| Alliant Reloder-26 | <<locked>> | 84% | 57,174 psi | 90% | 2913 fps | 100% |
| Alliant Reloder-33 | <<locked>> | 96% | 54,694 psi | 86% | 2949 fps | 98.7% |
| Alliant Reloder-50ᴾ | <<locked>> | 100% | 54,346 psi | 85% | 2936 fps | 98.3% |
| Baschieri & Pellagri 109 | <<locked>> | 88% | 54,563 psi | 86% | 2835 fps | 98.7% |
| Bofors RP15 | <<locked>> | 90% | 57,638 psi | 90% | 2910 fps | 100% |
| Bofors RP30 | <<locked>> | 94% | 56,695 psi | 89% | 2923 fps | 100% |
| Bofors RP5 | <<locked>> | 86% | 54,636 psi | 86% | 2867 fps | 100% |
| Hodgdon H1000 | <<locked>> | 92% | 54,317 psi | 85% | 2874 fps | 100% |
| Hodgdon H4831 | <<locked>> | 86% | 56,985 psi | 89% | 2864 fps | 99.9% |
| Hodgdon H4831 SC | <<locked>> | 86% | 55,869 psi | 88% | 2848 fps | 99.8% |
| Hodgdon Hybrid 100V | <<locked>> | 82% | 56,057 psi | 88% | 2759 fps | 100% |
| Hodgdon Retumbo | <<locked>> | 92% | 56,043 psi | 88% | 2992 fps | 100% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 37,797 psi | 59% | 1804 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 86% | 57,217 psi | 90% | 2838 fps | 99.9% |
| IMR 7828 SSC | <<locked>> | 88% | 56,434 psi | 88% | 2913 fps | 100% |
| IMR 7977 Enduron | <<locked>> | 92% | 55,767 psi | 87% | 2789 fps | 95.9% |
| IMR 8133 Enduronᴾ | <<locked>> | 100% | 54,549 psi | 85% | 2913 fps | 100% |
| Lovex S071 | <<locked>> | 92% | 56,434 psi | 88% | 2799 fps | 100% |
| Norma 217ᴾ | <<locked>> | 100% | 55,854 psi | 88% | 2933 fps | 100% |
| Norma MRP | <<locked>> | 84% | 54,636 psi | 86% | 2881 fps | 100% |
| Ramshot Grand | <<locked>> | 88% | 57,711 psi | 90% | 2936 fps | 100% |
| Ramshot Magnum | <<locked>> | 90% | 56,014 psi | 88% | 2864 fps | 100% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 38,841 psi | 61% | 1850 fps | 100% |
| ReloadSwiss RS 76 | <<locked>> | 92% | 56,840 psi | 89% | 2979 fps | 100% |
| ReloadSwiss RS 80 | <<locked>> | 94% | 56,086 psi | 88% | 2953 fps | 99.8% |
| Rottweil R 904 | <<locked>> | 84% | 56,188 psi | 88% | 2825 fps | 100% |
| Rottweil R 905 | <<locked>> | 84% | 55,027 psi | 86% | 2838 fps | 100% |
| SNPE Vectan SP 13ᴾ | <<locked>> | 100% | 47,268 psi | 74% | 2743 fps | 96.2% |
| SNPE Vectan Tubal 8000 | <<locked>> | 84% | 54,694 psi | 86% | 2835 fps | 100% |
| Somchem S361 | <<locked>> | 84% | 57,537 psi | 90% | 2818 fps | 99.9% |
| Somchem S385 | <<locked>> | 84% | 55,332 psi | 87% | 2805 fps | 100% |
| Vihtavuori N165 | <<locked>> | 88% | 55,230 psi | 87% | 2795 fps | 100% |
| Vihtavuori N170 | <<locked>> | 92% | 54,360 psi | 85% | 2822 fps | 97.3% |
| Vihtavuori N555 | <<locked>> | 84% | 54,737 psi | 86% | 2802 fps | 100% |
| Vihtavuori N560 | <<locked>> | 84% | 54,099 psi | 85% | 2887 fps | 99.8% |
| Vihtavuori N565 | <<locked>> | 90% | 55,056 psi | 86% | 2881 fps | 99.9% |
| Vihtavuori N568 | <<locked>> | 94% | 56,565 psi | 89% | 2953 fps | 99.7% |
| Vihtavuori N570 | <<locked>> | 94% | 53,882 psi | 84% | 2953 fps | 98.3% |
| Winchester StaBALL HD | <<locked>> | 88% | 56,826 psi | 89% | 2917 fps | 100% |
| Winchester Supreme 780 | <<locked>> | 86% | 55,071 psi | 86% | 2805 fps | 100% |
Recommended = one of the top powders for this cartridge and bullet combination.
Start Load - Barrel Length: 26"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| Accurate 3100 | <<locked>> | 80% | 44,701 psi | 70% | 2618 fps | 100% |
| Accurate 8700 | <<locked>> | 98% | 41,989 psi | 66% | 2664 fps | 95% |
| Accurate MAGPRO | <<locked>> | 80% | 46,412 psi | 73% | 2756 fps | 98.5% |
| ADI AR 2209 | <<locked>> | 80% | 48,747 psi | 76% | 2746 fps | 99.9% |
| ADI AR 2213 | <<locked>> | 80% | 43,932 psi | 69% | 2697 fps | 98.9% |
| ADI AR 2217 | <<locked>> | 80% | 32,837 psi | 51% | 2448 fps | 96% |
| ADI AR 2218 | <<locked>> | 92% | 42,540 psi | 67% | 2756 fps | 95.7% |
| ADI AR 2225 | <<locked>> | 80% | 30,124 psi | 47% | 2421 fps | 98% |
| Alliant Reloder-19 | <<locked>> | 80% | 48,588 psi | 76% | 2740 fps | 99.9% |
| Alliant Reloder-22 | <<locked>> | 80% | 44,701 psi | 70% | 2700 fps | 99.6% |
| Alliant Reloder-23 | <<locked>> | 80% | 43,555 psi | 68% | 2631 fps | 100% |
| Alliant Reloder-25 | <<locked>> | 80% | 37,724 psi | 59% | 2582 fps | 100% |
| Alliant Reloder-26 | <<locked>> | 80% | 49,400 psi | 77% | 2802 fps | 100% |
| Alliant Reloder-33 | 111.7 gr | 88% | 40,625 psi | 64% | 2687 fps | 95.2% |
| Alliant Reloder-50 | <<locked>> | 94% | 43,410 psi | 68% | 2736 fps | 95.6% |
| Baschieri & Pellagri 109 | <<locked>> | 80% | 42,279 psi | 66% | 2608 fps | 96% |
| Bofors RP15 | <<locked>> | 80% | 41,669 psi | 65% | 2641 fps | 99.2% |
| Bofors RP30 | <<locked>> | 80% | 35,230 psi | 55% | 2523 fps | 97.1% |
| Bofors RP5 | <<locked>> | 80% | 44,701 psi | 70% | 2700 fps | 99.6% |
| Hodgdon H1000 | <<locked>> | 80% | 35,621 psi | 56% | 2520 fps | 97.7% |
| Hodgdon H4831 | <<locked>> | 80% | 46,470 psi | 73% | 2690 fps | 98.8% |
| Hodgdon H4831 SC | <<locked>> | 80% | 45,643 psi | 72% | 2674 fps | 98.7% |
| Hodgdon Hybrid 100V | <<locked>> | 80% | 52,504 psi | 82% | 2710 fps | 100% |
| Hodgdon Retumbo | 94.1 gr | 80% | 36,854 psi | 58% | 2635 fps | 99.1% |
| Hodgdon TrailBoss | <<locked>> | 80% | 28,369 psi | 44% | 1614 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 80% | 47,355 psi | 74% | 2677 fps | 99.1% |
| IMR 7828 SSC | <<locked>> | 80% | 42,714 psi | 67% | 2680 fps | 98.7% |
| IMR 7977 Enduron | <<locked>> | 90% | 52,214 psi | 82% | 2733 fps | 95.1% |
| IMR 8133 Enduron | <<locked>> | 84% | 31,705 psi | 50% | 2454 fps | 95.5% |
| Lovex S071 | <<locked>> | 80% | 38,566 psi | 60% | 2503 fps | 99.9% |
| Norma 217 | <<locked>> | 80% | 27,876 psi | 44% | 2365 fps | 96% |
| Norma MRP | <<locked>> | 80% | 47,616 psi | 75% | 2769 fps | 100% |
| Ramshot Grand | <<locked>> | 80% | 42,873 psi | 67% | 2694 fps | 99% |
| Ramshot Magnum | <<locked>> | 80% | 38,667 psi | 61% | 2572 fps | 99.3% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 29,138 psi | 46% | 1654 fps | 100% |
| ReloadSwiss RS 76 | <<locked>> | 80% | 36,100 psi | 57% | 2608 fps | 99.6% |
| ReloadSwiss RS 80 | <<locked>> | 82% | 35,694 psi | 56% | 2566 fps | 95.7% |
| Rottweil R 904 | <<locked>> | 80% | 49,443 psi | 77% | 2717 fps | 99.6% |
| Rottweil R 905 | <<locked>> | 80% | 48,298 psi | 76% | 2730 fps | 99.9% |
| SNPE Vectan SP 13 | <<locked>> | 98% | 44,106 psi | 69% | 2684 fps | 95.3% |
| SNPE Vectan Tubal 8000 | <<locked>> | 80% | 47,964 psi | 75% | 2726 fps | 99.9% |
| Somchem S361 | <<locked>> | 80% | 50,372 psi | 79% | 2710 fps | 99.3% |
| Somchem S385 | <<locked>> | 80% | 48,617 psi | 76% | 2703 fps | 100% |
| Vihtavuori N165 | <<locked>> | 80% | 42,569 psi | 67% | 2585 fps | 99.6% |
| Vihtavuori N170 | <<locked>> | 88% | 47,514 psi | 74% | 2703 fps | 95.6% |
| Vihtavuori N555 | <<locked>> | 80% | 48,254 psi | 76% | 2707 fps | 100% |
| Vihtavuori N560 | <<locked>> | 80% | 47,224 psi | 74% | 2766 fps | 99.1% |
| Vihtavuori N565 | <<locked>> | 80% | 39,262 psi | 62% | 2592 fps | 97.6% |
| Vihtavuori N568 | <<locked>> | 82% | 36,912 psi | 58% | 2582 fps | 95.5% |
| Vihtavuori N570 | 107.4 gr | 88% | 43,511 psi | 68% | 2759 fps | 95.8% |
| Winchester StaBALL HD | <<locked>> | 80% | 42,018 psi | 66% | 2697 fps | 100% |
| Winchester Supreme 780 | <<locked>> | 80% | 44,831 psi | 70% | 2638 fps | 99.6% |
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 52 powders for .338-378 Weath. Mag. loaded with the .338 | 250gr | Speer Grand Slam. ADI AR 2218 delivers the highest muzzle velocity at 3,035 fps; across all powders the maximum-charge window runs from 1,804 fps to 3,035 fps. Accurate 8700 gives the best case fill at 100 %, and 52 of the 52 powders fall inside the usable 80–100 % fill window.
Relative to the caliber's maximum pressure (440 MPa), the top charges use 59–90 %, leaving at least 10 % headroom. The 250.0 gr projectile in 0.338" calls for a 1:6.0 twist; slower twists will usually not stabilise this weight. Accurate 8700, ADI AR 2218, Alliant Reloder-50 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. Vihtavuori N570, Alliant Reloder-33, Hodgdon Retumbo rank at the top here: for .338-378 Weath. Mag. with the .338 | 250gr | Speer Grand Slam 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.