Load Specifications
Load data in caliber .45-70 Govt. with .458 | 300gr | X-TREME RNFP bullet and 4 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are ReloadSwiss RS 14 and 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 ≥ 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: 24"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| ADI AR 2207 | <<locked>> | 84% | 28,210 psi | 88% | 2077 fps | 97.4% |
| Hodgdon TrailBoss | <<locked>> | 98% | 28,166 psi | 88% | 1401 fps | 100% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 28,282 psi | 89% | 1447 fps | 100% |
| Vihtavuori N120 | <<locked>> | 84% | 28,616 psi | 90% | 2057 fps | 98.5% |
Recommended = one of the top powders for this cartridge and bullet combination.
Start Load - Barrel Length: 24"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| ADI AR 2207 | <<locked>> | 80% | 24,990 psi | 78% | 1998 fps | 96.1% |
| Hodgdon TrailBoss | 15.9 gr | 80% | 21,132 psi | 66% | 1266 fps | 100% |
| ReloadSwiss RS 14 | 16.2 gr | 80% | 20,697 psi | 65% | 1296 fps | 100% |
| Vihtavuori N120 | <<locked>> | 80% | 25,382 psi | 80% | 1978 fps | 97.4% |
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 11 powders for .45-70 Govt. loaded with the .458 | 300gr | X-TREME RNFP. ADI AR 2207 delivers the highest muzzle velocity at 2,077 fps; across all powders the maximum-charge window runs from 1,401 fps to 2,077 fps. ReloadSwiss RS 14 gives the best case fill at 100 %, and 11 of the 11 powders fall inside the usable 80–100 % fill window.
Relative to the caliber's maximum pressure (220 MPa), the top charges use 85–90 %, leaving at least 10 % headroom. 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. ReloadSwiss RS 14, Hodgdon TrailBoss rank at the top here: for .45-70 Govt. with the .458 | 300gr | X-TREME RNFP they combine a high case fill with complete burn and sit in the upper velocity band. As outliers, Accurate 2015, Alliant AR-Comp, Alliant Reloder-10x burn incompletely and react more sensitively to barrel length and temperature. Always begin at the start load and work up in small increments while checking case and primer for pressure signs.