Load Specifications
Load data in caliber .455 MK II with .452 | 200gr | Rim Rock RNFP Cowboy bullet and 5 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are Hodgdon TrailBoss.
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 ≥ 60% and propellant combustion ≥ 80%. 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: 4"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| Baschieri & Pellagri 102 Pistol² | <<locked>> | 72% | 10,805 psi | 83% | 741 fps | 96.9% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 9,384 psi | 72% | 673 fps | 98% |
| Maxam CSB 2² | <<locked>> | 64% | 11,487 psi | 88% | 787 fps | 96.6% |
| ReloadSwiss RS 14*ᴾ | <<locked>> | 100% | 8,093 psi | 62% | 643 fps | 92% |
| Vihtavuori N32C Tin Star | <<locked>> | 80% | 11,023 psi | 84% | 722 fps | 100% |
Recommended = one of the top powders for this cartridge and bullet combination.
Start Load - Barrel Length: 4"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| Baschieri & Pellagri 102 Pistol*² | <<locked>> | 60% | 8,050 psi | 62% | 653 fps | 92.6% |
| Hodgdon TrailBoss*² | 2.5 gr | 60% | 4,598 psi | 35% | 476 fps | 86.7% |
| Maxam CSB 2*² | <<locked>> | 60% | 10,124 psi | 78% | 748 fps | 94.9% |
| ReloadSwiss RS 14* | <<locked>> | 80% | 6,005 psi | 46% | 558 fps | 86.3% |
| Vihtavuori N32C Tin Star² | <<locked>> | 60% | 6,889 psi | 53% | 597 fps | 98.3% |
Recommended = one of the top powders for this cartridge and bullet combination.
* not dangerous but load has suboptimal powder burnt with possible characteristics such as extensive muzzle flash or inaccurate loads.
² fill rate low - you might want to consider using a filler to ensure proper ignition.
ᴾ possible press load - work up slowly to this load while watching for signs of excessive pressure.
This overview compares 5 powders for .455 MK II loaded with the .452 | 200gr | Rim Rock RNFP Cowboy. Maxam CSB 2 delivers the highest muzzle velocity at 787 fps; across all powders the maximum-charge window runs from 643 fps to 787 fps. Hodgdon TrailBoss gives the best case fill at 100 %, and 3 of the 5 powders fall inside the usable 80–100 % fill window.
Relative to the caliber's maximum pressure (90 MPa), the top charges use 62–88 %, leaving at least 12 % 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. Hodgdon TrailBoss rank at the top here: for .455 MK II with the .452 | 200gr | Rim Rock RNFP Cowboy they combine a high case fill with complete burn and sit in the upper velocity band. As outliers, ReloadSwiss RS 14 burn incompletely and react more sensitively to barrel length and temperature. Baschieri & Pellagri 102 Pistol, Hodgdon TrailBoss, Maxam CSB 2 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.