Load Specifications
Load data in caliber .38-55 Win. with .38 | 240gr | Rim Rock RNFP Cowboy 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.
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: 20"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| ADI AR 2207 | <<locked>> | 90% | 30,850 psi | 89% | 1890 fps | 97.9% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 27,847 psi | 80% | 1227 fps | 100% |
| Lovex S053 | <<locked>> | 82% | 30,342 psi | 87% | 1801 fps | 99.1% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 26,919 psi | 77% | 1250 fps | 100% |
| ReloadSwiss RS 36 | <<locked>> | 82% | 30,008 psi | 86% | 1824 fps | 96% |
| SNPE Vectan BA6 1/2 | <<locked>> | 84% | 30,618 psi | 88% | 1726 fps | 100% |
| Vihtavuori N120 | <<locked>> | 90% | 31,357 psi | 90% | 1870 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 | 27 gr | 82% | 23,743 psi | 68% | 1736 fps | 95% |
| Hodgdon TrailBoss | <<locked>> | 80% | 19,957 psi | 57% | 1093 fps | 100% |
| Lovex S053 | <<locked>> | 80% | 28,631 psi | 82% | 1768 fps | 98.7% |
| ReloadSwiss RS 14 | 9.7 gr | 80% | 19,377 psi | 56% | 1115 fps | 100% |
| ReloadSwiss RS 36 | <<locked>> | 80% | 28,369 psi | 82% | 1791 fps | 95.3% |
| SNPE Vectan BA6 1/2 | <<locked>> | 80% | 27,412 psi | 79% | 1673 fps | 100% |
| Vihtavuori N120 | 26.4 gr | 80% | 22,902 psi | 66% | 1690 fps | 95.9% |
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 .38 | 240gr | Rim Rock RNFP Cowboy. ADI AR 2207 delivers the highest muzzle velocity at 1,890 fps; across all powders the maximum-charge window runs from 1,227 fps to 1,890 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 77–90 %, 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 Cowboy 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.