Load Specifications
Load data in caliber 7.21 Firebird with .284 | 139gr | Hornady InterLock FP bullet and 50 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are Hodgdon Retumbo, ADI AR 2218 and Vihtavuori N570.
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: 26"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| Accurate 3100 | <<locked>> | 84% | 56,913 psi | 85% | 3163 fps | 100% |
| Accurate 8700ᴾ | <<locked>> | 100% | 53,693 psi | 80% | 3192 fps | 97.7% |
| Accurate MAGPRO | <<locked>> | 84% | 60,350 psi | 90% | 3346 fps | 99.8% |
| ADI AR 2209 | <<locked>> | 82% | 57,638 psi | 86% | 3258 fps | 100% |
| ADI AR 2213 | <<locked>> | 84% | 56,695 psi | 85% | 3274 fps | 99.9% |
| ADI AR 2217 | <<locked>> | 92% | 56,449 psi | 85% | 3255 fps | 100% |
| ADI AR 2218 | <<locked>> | 96% | 57,580 psi | 86% | 3392 fps | 99.1% |
| ADI AR 2225 | <<locked>> | 94% | 56,492 psi | 85% | 3281 fps | 100% |
| Alliant Reloder-19 | <<locked>> | 82% | 57,261 psi | 86% | 3245 fps | 100% |
| Alliant Reloder-22 | <<locked>> | 84% | 57,276 psi | 86% | 3271 fps | 100% |
| Alliant Reloder-23 | <<locked>> | 86% | 59,437 psi | 89% | 3225 fps | 100% |
| Alliant Reloder-25 | <<locked>> | 88% | 56,608 psi | 85% | 3248 fps | 100% |
| Alliant Reloder-33 | <<locked>> | 94% | 59,872 psi | 90% | 3366 fps | 99.1% |
| Alliant Reloder-50 | <<locked>> | 96% | 56,014 psi | 84% | 3281 fps | 98.1% |
| Baschieri & Pellagri 109 | <<locked>> | 86% | 56,855 psi | 85% | 3228 fps | 98.8% |
| Bofors RP15 | <<locked>> | 86% | 56,840 psi | 85% | 3261 fps | 100% |
| Bofors RP30 | <<locked>> | 90% | 56,652 psi | 85% | 3274 fps | 100% |
| Bofors RP5 | <<locked>> | 84% | 57,276 psi | 86% | 3271 fps | 100% |
| Hodgdon H1000 | <<locked>> | 90% | 57,885 psi | 87% | 3278 fps | 100% |
| Hodgdon H4831 | <<locked>> | 84% | 59,103 psi | 89% | 3264 fps | 99.9% |
| Hodgdon H4831 SC | <<locked>> | 84% | 58,015 psi | 87% | 3248 fps | 99.8% |
| Hodgdon Retumbo | <<locked>> | 88% | 56,333 psi | 84% | 3346 fps | 100% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 37,956 psi | 57% | 2142 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 84% | 58,798 psi | 88% | 3235 fps | 99.9% |
| IMR 7828 SSC | <<locked>> | 86% | 59,379 psi | 89% | 3323 fps | 100% |
| IMR 7977 Enduron | <<locked>> | 90% | 57,638 psi | 86% | 3182 fps | 96.1% |
| IMR 8133 Enduron | <<locked>> | 98% | 59,393 psi | 89% | 3327 fps | 100% |
| Lovex S071 | <<locked>> | 90% | 59,117 psi | 89% | 3196 fps | 100% |
| Norma 217 | <<locked>> | 96% | 56,985 psi | 85% | 3284 fps | 100% |
| Norma MRP | <<locked>> | 82% | 57,537 psi | 86% | 3281 fps | 100% |
| Ramshot Grand | <<locked>> | 84% | 56,956 psi | 85% | 3284 fps | 100% |
| Ramshot Magnum | <<locked>> | 88% | 59,886 psi | 90% | 3268 fps | 100% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 39,001 psi | 58% | 2192 fps | 100% |
| ReloadSwiss RS 76 | <<locked>> | 88% | 57,464 psi | 86% | 3327 fps | 100% |
| ReloadSwiss RS 80 | <<locked>> | 90% | 56,710 psi | 85% | 3294 fps | 99.7% |
| Rottweil R 904 | <<locked>> | 82% | 57,696 psi | 86% | 3222 fps | 99.9% |
| Rottweil R 905 | <<locked>> | 82% | 57,145 psi | 86% | 3238 fps | 100% |
| SNPE Vectan SP 13ᴾ | <<locked>> | 100% | 55,390 psi | 83% | 3205 fps | 97.7% |
| SNPE Vectan Tubal 8000 | <<locked>> | 82% | 56,782 psi | 85% | 3235 fps | 100% |
| Somchem S361 | <<locked>> | 82% | 59,277 psi | 89% | 3209 fps | 99.9% |
| Somchem S385 | <<locked>> | 82% | 57,348 psi | 86% | 3199 fps | 100% |
| Vihtavuori N165 | <<locked>> | 86% | 57,696 psi | 86% | 3189 fps | 100% |
| Vihtavuori N170 | <<locked>> | 90% | 57,421 psi | 86% | 3222 fps | 97.5% |
| Vihtavuori N555 | <<locked>> | 82% | 57,072 psi | 86% | 3199 fps | 100% |
| Vihtavuori N560 | <<locked>> | 82% | 56,753 psi | 85% | 3287 fps | 99.8% |
| Vihtavuori N565 | <<locked>> | 88% | 58,479 psi | 88% | 3284 fps | 99.9% |
| Vihtavuori N568 | <<locked>> | 90% | 56,811 psi | 85% | 3301 fps | 99.5% |
| Vihtavuori N570 | <<locked>> | 92% | 58,494 psi | 88% | 3373 fps | 98.6% |
| Winchester StaBALL HD | <<locked>> | 84% | 57,087 psi | 86% | 3264 fps | 100% |
| Winchester Supreme 780 | <<locked>> | 84% | 57,363 psi | 86% | 3199 fps | 100% |
Recommended = one of the top powders for this cartridge and bullet combination.
Start Load - Barrel Length: 26"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| Accurate 3100 | <<locked>> | 80% | 49,734 psi | 75% | 3045 fps | 100% |
| Accurate 8700 | <<locked>> | 96% | 46,137 psi | 69% | 3048 fps | 95.7% |
| Accurate MAGPRO | <<locked>> | 80% | 52,272 psi | 78% | 3205 fps | 99% |
| ADI AR 2209 | <<locked>> | 80% | 53,751 psi | 81% | 3192 fps | 100% |
| ADI AR 2213 | <<locked>> | 80% | 49,298 psi | 74% | 3140 fps | 99.3% |
| ADI AR 2217 | <<locked>> | 80% | 36,854 psi | 55% | 2854 fps | 96.7% |
| ADI AR 2218 | 103.1 gr | 90% | 45,905 psi | 69% | 3150 fps | 96.3% |
| ADI AR 2225 | <<locked>> | 80% | 34,214 psi | 51% | 2822 fps | 98.6% |
| Alliant Reloder-19 | <<locked>> | 80% | 53,563 psi | 80% | 3182 fps | 100% |
| Alliant Reloder-22 | <<locked>> | 80% | 50,053 psi | 75% | 3140 fps | 99.8% |
| Alliant Reloder-23 | <<locked>> | 80% | 48,559 psi | 73% | 3054 fps | 100% |
| Alliant Reloder-25 | <<locked>> | 80% | 42,757 psi | 64% | 3002 fps | 100% |
| Alliant Reloder-33 | <<locked>> | 86% | 44,251 psi | 66% | 3061 fps | 95.5% |
| Alliant Reloder-50 | <<locked>> | 90% | 44,759 psi | 67% | 3054 fps | 95.1% |
| Baschieri & Pellagri 109 | <<locked>> | 80% | 46,630 psi | 70% | 3031 fps | 96.7% |
| Bofors RP15 | <<locked>> | 80% | 46,499 psi | 70% | 3071 fps | 99.5% |
| Bofors RP30 | <<locked>> | 80% | 40,016 psi | 60% | 2936 fps | 97.7% |
| Bofors RP5 | <<locked>> | 80% | 50,053 psi | 75% | 3140 fps | 99.8% |
| Hodgdon H1000 | <<locked>> | 80% | 40,219 psi | 60% | 2940 fps | 98.4% |
| Hodgdon H4831 | <<locked>> | 80% | 51,488 psi | 77% | 3133 fps | 99.2% |
| Hodgdon H4831 SC | <<locked>> | 80% | 50,647 psi | 76% | 3117 fps | 99.1% |
| Hodgdon Retumbo | 86.5 gr | 80% | 42,018 psi | 63% | 3071 fps | 99.5% |
| Hodgdon TrailBoss | <<locked>> | 80% | 28,558 psi | 43% | 1926 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 80% | 51,677 psi | 77% | 3114 fps | 99.3% |
| IMR 7828 SSC | <<locked>> | 80% | 48,022 psi | 72% | 3123 fps | 99.1% |
| IMR 7977 Enduron | <<locked>> | 88% | 54,070 psi | 81% | 3120 fps | 95.2% |
| IMR 8133 Enduron | <<locked>> | 82% | 34,040 psi | 51% | 2795 fps | 95.3% |
| Lovex S071 | <<locked>> | 80% | 42,801 psi | 64% | 2913 fps | 100% |
| Norma 217 | <<locked>> | 80% | 32,242 psi | 48% | 2759 fps | 96.8% |
| Norma MRP | <<locked>> | 80% | 53,679 psi | 80% | 3219 fps | 100% |
| Ramshot Grand | <<locked>> | 80% | 48,936 psi | 73% | 3143 fps | 99.5% |
| Ramshot Magnum | <<locked>> | 80% | 44,280 psi | 66% | 2999 fps | 99.7% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 29,298 psi | 44% | 1969 fps | 100% |
| ReloadSwiss RS 76 | <<locked>> | 80% | 41,945 psi | 63% | 3045 fps | 99.9% |
| ReloadSwiss RS 80 | <<locked>> | 80% | 38,580 psi | 58% | 2920 fps | 95.7% |
| Rottweil R 904 | <<locked>> | 80% | 54,085 psi | 81% | 3163 fps | 99.8% |
| Rottweil R 905 | <<locked>> | 80% | 53,476 psi | 80% | 3176 fps | 100% |
| SNPE Vectan SP 13 | <<locked>> | 96% | 48,153 psi | 72% | 3071 fps | 95.9% |
| SNPE Vectan Tubal 8000 | <<locked>> | 80% | 53,127 psi | 80% | 3173 fps | 100% |
| Somchem S361 | <<locked>> | 80% | 55,419 psi | 83% | 3146 fps | 99.6% |
| Somchem S385 | <<locked>> | 80% | 53,809 psi | 81% | 3140 fps | 100% |
| Vihtavuori N165 | <<locked>> | 80% | 47,195 psi | 71% | 3009 fps | 99.8% |
| Vihtavuori N170 | <<locked>> | 86% | 50,067 psi | 75% | 3084 fps | 95.8% |
| Vihtavuori N555 | <<locked>> | 80% | 53,490 psi | 80% | 3140 fps | 100% |
| Vihtavuori N560 | <<locked>> | 80% | 52,982 psi | 79% | 3219 fps | 99.5% |
| Vihtavuori N565 | <<locked>> | 80% | 44,454 psi | 67% | 3018 fps | 98.2% |
| Vihtavuori N568 | <<locked>> | 80% | 39,450 psi | 59% | 2940 fps | 95.4% |
| Vihtavuori N570 | 96.5 gr | 86% | 47,021 psi | 70% | 3146 fps | 95.9% |
| Winchester StaBALL HD | <<locked>> | 80% | 48,979 psi | 73% | 3136 fps | 100% |
| Winchester Supreme 780 | <<locked>> | 80% | 49,893 psi | 75% | 3071 fps | 99.8% |
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 57 powders for 7.21 Firebird loaded with the .284 | 139gr | Hornady InterLock FP. ADI AR 2218 delivers the highest muzzle velocity at 3,392 fps; across all powders the maximum-charge window runs from 2,142 fps to 3,392 fps. Accurate 8700 gives the best case fill at 100 %, and 57 of the 57 powders fall inside the usable 80–100 % fill window.
Relative to the caliber's maximum pressure (460 MPa), the top charges use 57–90 %, leaving at least 10 % headroom. The 139.0 gr projectile in 0.284" calls for a 1:15.5 twist; slower twists will usually not stabilise this weight. Accurate 8700, Hodgdon TrailBoss, Hodgdon US 869 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 Retumbo, ADI AR 2218, Vihtavuori N570 rank at the top here: for 7.21 Firebird with the .284 | 139gr | Hornady InterLock FP they combine a high case fill with complete burn and sit in the upper velocity band. As outliers, Hodgdon 50BMG, Hodgdon US 869, Ramshot LRT 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.