Load Specifications
Load data in caliber .38-55 Win. with .38 | 240gr | Rim Rock RNFP?3LG FB Cowboy bullet and 8 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% | 29,588 psi | 85% | 1854 fps | 97.3% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 27,470 psi | 79% | 1211 fps | 100% |
| IMR 4227 | <<locked>> | 82% | 30,763 psi | 88% | 1785 fps | 96.1% |
| Lovex S053 | <<locked>> | 84% | 31,314 psi | 90% | 1804 fps | 99.2% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 26,527 psi | 76% | 1237 fps | 100% |
| ReloadSwiss RS 36 | <<locked>> | 84% | 31,096 psi | 89% | 1831 fps | 96.1% |
| SNPE Vectan BA6 1/2 | <<locked>> | 86% | 31,488 psi | 90% | 1729 fps | 100% |
| Vihtavuori N120 | <<locked>> | 92% | 29,791 psi | 86% | 1827 fps | 98.4% |
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 | 26.8 gr | 84% | 24,511 psi | 70% | 1742 fps | 95.1% |
| Hodgdon TrailBoss | <<locked>> | 80% | 19,725 psi | 57% | 1079 fps | 100% |
| IMR 4227 | <<locked>> | 80% | 28,935 psi | 83% | 1749 fps | 95.4% |
| Lovex S053 | <<locked>> | 80% | 27,760 psi | 80% | 1739 fps | 98.3% |
| ReloadSwiss RS 14 | 9.4 gr | 80% | 19,145 psi | 55% | 1102 fps | 100% |
| ReloadSwiss RS 36 | <<locked>> | 82% | 29,022 psi | 83% | 1791 fps | 95.3% |
| SNPE Vectan BA6 1/2 | <<locked>> | 80% | 26,440 psi | 76% | 1644 fps | 100% |
| Vihtavuori N120 | 25.6 gr | 82% | 22,046 psi | 63% | 1657 fps | 95% |
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 14 powders for .38-55 Win. loaded with the .38 | 240gr | Rim Rock RNFP?3LG FB Cowboy. Alliant Reloder-10x delivers the highest muzzle velocity at 1,883 fps; across all powders the maximum-charge window runs from 1,211 fps to 1,883 fps. Hodgdon TrailBoss gives the best case fill at 100 %, and 14 of the 14 powders fall inside the usable 80–100 % fill window.
Relative to the caliber's maximum pressure (240 MPa), the top charges use 76–90 %, 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 .38 | 240gr | Rim Rock RNFP?3LG FB Cowboy they combine a high case fill with complete burn and sit in the upper velocity band. As outliers, Accurate 1680, Alliant Reloder-10x, Alliant Reloder-7 burn incompletely and react more sensitively to barrel length and temperature. 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.