Load Specifications
Load data in caliber .38-55 Win. with .378 | 255gr | ACME RNFP COATED bullet and 7 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are ADI AR 2207, Vihtavuori N120 and ReloadSwiss RS 14.
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: 20"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| ADI AR 2207 | <<locked>> | 90% | 31,328 psi | 90% | 1827 fps | 98.4% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 28,137 psi | 81% | 1178 fps | 100% |
| Lovex S053 | <<locked>> | 82% | 31,009 psi | 89% | 1742 fps | 99.5% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 27,267 psi | 78% | 1204 fps | 100% |
| ReloadSwiss RS 36 | <<locked>> | 82% | 30,603 psi | 88% | 1765 fps | 96.7% |
| SNPE Vectan BA6 1/2 | <<locked>> | 84% | 31,024 psi | 89% | 1660 fps | 100% |
| Vihtavuori N120 | <<locked>> | 88% | 30,008 psi | 86% | 1778 fps | 98.9% |
Recommended = one of the top powders for this cartridge and bullet combination.
Start Load - Barrel Length: 20"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| ADI AR 2207 | 25.4 gr | 80% | 22,713 psi | 65% | 1647 fps | 95% |
| Hodgdon TrailBoss | <<locked>> | 80% | 20,247 psi | 58% | 1050 fps | 100% |
| Lovex S053 | <<locked>> | 80% | 29,167 psi | 84% | 1709 fps | 99.1% |
| ReloadSwiss RS 14 | 9.3 gr | 80% | 19,406 psi | 56% | 1066 fps | 100% |
| ReloadSwiss RS 36 | <<locked>> | 80% | 28,848 psi | 83% | 1732 fps | 96% |
| SNPE Vectan BA6 1/2 | <<locked>> | 80% | 27,717 psi | 80% | 1608 fps | 100% |
| Vihtavuori N120 | 25.4 gr | 80% | 23,192 psi | 67% | 1634 fps | 96.6% |
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 7 powders for .38-55 Win. loaded with the .378 | 255gr | ACME RNFP COATED. ADI AR 2207 delivers the highest muzzle velocity at 1,827 fps; across all powders the maximum-charge window runs from 1,178 fps to 1,827 fps. Hodgdon TrailBoss gives the best case fill at 100 %, and 7 of the 7 powders fall inside the usable 80–100 % fill window.
Relative to the caliber's maximum pressure (240 MPa), the top charges use 78–90 %, leaving at least 10 % headroom. Hodgdon TrailBoss, ReloadSwiss RS 14 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. ADI AR 2207, Vihtavuori N120, ReloadSwiss RS 14 rank at the top here: for .38-55 Win. with the .378 | 255gr | ACME RNFP COATED they combine a high case fill with complete burn and sit in the upper velocity band. Hodgdon TrailBoss, ReloadSwiss RS 14 stay subsonic at start load. Always begin at the start load and work up in small increments while checking case and primer for pressure signs.