Load Specifications
Load data in caliber 7.21 Firebird with .284 | 158gr | Prvi Partizan Grom bullet and 53 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are ADI AR 2218, Vihtavuori N570 and IMR 8133 Enduron.
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% | 59,306 psi | 89% | 3038 fps | 100% |
| Accurate 8700ᴾ | <<locked>> | 100% | 56,246 psi | 84% | 3100 fps | 99% |
| Accurate MAGPRO | <<locked>> | 82% | 58,784 psi | 88% | 3163 fps | 100% |
| ADI AR 2209 | <<locked>> | 82% | 59,930 psi | 90% | 3130 fps | 100% |
| ADI AR 2213 | <<locked>> | 84% | 59,045 psi | 89% | 3153 fps | 100% |
| ADI AR 2217 | <<locked>> | 92% | 59,176 psi | 89% | 3143 fps | 100% |
| ADI AR 2218 | <<locked>> | 94% | 56,115 psi | 84% | 3219 fps | 99.5% |
| ADI AR 2225 | <<locked>> | 94% | 59,335 psi | 89% | 3163 fps | 100% |
| Alliant Reloder-19 | <<locked>> | 82% | 59,335 psi | 89% | 3117 fps | 100% |
| Alliant Reloder-22 | <<locked>> | 84% | 59,582 psi | 89% | 3143 fps | 100% |
| Alliant Reloder-23 | <<locked>> | 84% | 57,928 psi | 87% | 3038 fps | 100% |
| Alliant Reloder-25 | <<locked>> | 88% | 59,205 psi | 89% | 3123 fps | 100% |
| Alliant Reloder-33 | <<locked>> | 92% | 58,392 psi | 88% | 3196 fps | 99.5% |
| Alliant Reloder-50 | <<locked>> | 96% | 58,856 psi | 88% | 3192 fps | 99.3% |
| Baschieri & Pellagri 109 | <<locked>> | 86% | 58,972 psi | 88% | 3114 fps | 99.6% |
| Bofors RP15 | <<locked>> | 86% | 59,146 psi | 89% | 3136 fps | 100% |
| Bofors RP30 | <<locked>> | 90% | 59,234 psi | 89% | 3156 fps | 100% |
| Bofors RP5 | <<locked>> | 84% | 59,582 psi | 89% | 3143 fps | 100% |
| Hodgdon H1000 | <<locked>> | 88% | 56,463 psi | 85% | 3097 fps | 100% |
| Hodgdon H4831 | <<locked>> | 82% | 57,348 psi | 86% | 3077 fps | 100% |
| Hodgdon H4831 SC | <<locked>> | 84% | 60,176 psi | 90% | 3123 fps | 100% |
| Hodgdon Retumbo | <<locked>> | 88% | 59,437 psi | 89% | 3232 fps | 100% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 38,159 psi | 57% | 2011 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 82% | 57,203 psi | 86% | 3054 fps | 100% |
| IMR 7828 SSC | <<locked>> | 84% | 57,914 psi | 87% | 3140 fps | 100% |
| IMR 7977 Enduron | <<locked>> | 90% | 59,799 psi | 90% | 3071 fps | 97.5% |
| IMR 8133 Enduron | <<locked>> | 96% | 58,175 psi | 87% | 3153 fps | 100% |
| Lovex D100 | <<locked>> | 92% | 57,696 psi | 86% | 3061 fps | 96.2% |
| Lovex S071 | <<locked>> | 88% | 57,783 psi | 87% | 3015 fps | 100% |
| Norma 217 | <<locked>> | 96% | 59,872 psi | 90% | 3169 fps | 100% |
| Norma MRP | <<locked>> | 82% | 60,046 psi | 90% | 3156 fps | 100% |
| Ramshot Grand | <<locked>> | 84% | 59,640 psi | 89% | 3166 fps | 100% |
| Ramshot LRT | <<locked>> | 96% | 59,799 psi | 90% | 3212 fps | 96.4% |
| Ramshot Magnum | <<locked>> | 86% | 58,175 psi | 87% | 3084 fps | 100% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 39,276 psi | 59% | 2060 fps | 100% |
| ReloadSwiss RS 76 | <<locked>> | 86% | 56,101 psi | 84% | 3146 fps | 100% |
| ReloadSwiss RS 80 | <<locked>> | 90% | 59,379 psi | 89% | 3189 fps | 100% |
| Rottweil R 904 | <<locked>> | 82% | 59,756 psi | 90% | 3094 fps | 100% |
| Rottweil R 905 | <<locked>> | 82% | 59,466 psi | 89% | 3110 fps | 100% |
| Shooters World 50 BMG | <<locked>> | 92% | 57,696 psi | 86% | 3061 fps | 96.2% |
| SNPE Vectan SP 13ᴾ | <<locked>> | 100% | 57,841 psi | 87% | 3104 fps | 98.9% |
| SNPE Vectan Tubal 8000 | <<locked>> | 82% | 59,103 psi | 89% | 3107 fps | 100% |
| Somchem S385 | <<locked>> | 82% | 59,509 psi | 89% | 3071 fps | 100% |
| Vihtavuori 20N29ᴾ | <<locked>> | 100% | 51,126 psi | 77% | 3009 fps | 96.2% |
| Vihtavuori N165 | <<locked>> | 86% | 59,799 psi | 90% | 3061 fps | 100% |
| Vihtavuori N170 | <<locked>> | 90% | 59,654 psi | 89% | 3110 fps | 98.7% |
| Vihtavuori N555 | <<locked>> | 82% | 59,582 psi | 89% | 3068 fps | 100% |
| Vihtavuori N560 | <<locked>> | 82% | 59,190 psi | 89% | 3169 fps | 100% |
| Vihtavuori N565 | <<locked>> | 86% | 57,101 psi | 86% | 3110 fps | 100% |
| Vihtavuori N568 | <<locked>> | 90% | 59,480 psi | 89% | 3189 fps | 100% |
| Vihtavuori N570 | <<locked>> | 90% | 57,145 psi | 86% | 3196 fps | 99.1% |
| Winchester StaBALL HD | <<locked>> | 84% | 60,031 psi | 90% | 3140 fps | 100% |
| Winchester Supreme 780 | <<locked>> | 84% | 59,640 psi | 89% | 3074 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% | 51,909 psi | 78% | 2927 fps | 100% |
| Accurate 8700 | <<locked>> | 92% | 41,771 psi | 63% | 2828 fps | 95.5% |
| Accurate MAGPRO | <<locked>> | 80% | 54,766 psi | 82% | 3097 fps | 99.8% |
| ADI AR 2209 | <<locked>> | 80% | 55,970 psi | 84% | 3068 fps | 100% |
| ADI AR 2213 | <<locked>> | 80% | 51,488 psi | 77% | 3028 fps | 99.9% |
| ADI AR 2217 | <<locked>> | 80% | 38,740 psi | 58% | 2769 fps | 98.5% |
| ADI AR 2218 | 94.3 gr | 86% | 41,466 psi | 62% | 2913 fps | 96% |
| ADI AR 2225 | <<locked>> | 80% | 36,056 psi | 54% | 2743 fps | 99.7% |
| Alliant Reloder-19 | <<locked>> | 80% | 55,738 psi | 84% | 3058 fps | 100% |
| Alliant Reloder-22 | <<locked>> | 80% | 52,214 psi | 78% | 3025 fps | 100% |
| Alliant Reloder-23 | <<locked>> | 80% | 50,894 psi | 76% | 2933 fps | 100% |
| Alliant Reloder-25 | <<locked>> | 80% | 45,020 psi | 67% | 2897 fps | 100% |
| Alliant Reloder-33 | <<locked>> | 82% | 40,103 psi | 60% | 2831 fps | 95.3% |
| Alliant Reloder-50 | <<locked>> | 88% | 43,772 psi | 66% | 2907 fps | 96.1% |
| Baschieri & Pellagri 109 | <<locked>> | 80% | 48,327 psi | 72% | 2927 fps | 98.1% |
| Bofors RP15 | <<locked>> | 80% | 48,602 psi | 73% | 2963 fps | 100% |
| Bofors RP30 | <<locked>> | 80% | 42,119 psi | 63% | 2848 fps | 99.1% |
| Bofors RP5 | <<locked>> | 80% | 52,214 psi | 78% | 3025 fps | 100% |
| Hodgdon H1000 | <<locked>> | 80% | 42,279 psi | 63% | 2844 fps | 99.5% |
| Hodgdon H4831 | <<locked>> | 80% | 53,548 psi | 80% | 3018 fps | 99.8% |
| Hodgdon H4831 SC | <<locked>> | 80% | 52,692 psi | 79% | 3002 fps | 99.8% |
| Hodgdon Retumbo | <<locked>> | 80% | 44,382 psi | 67% | 2972 fps | 100% |
| Hodgdon TrailBoss | <<locked>> | 80% | 28,747 psi | 43% | 1804 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 80% | 53,606 psi | 80% | 2992 fps | 99.9% |
| IMR 7828 SSC | <<locked>> | 80% | 50,241 psi | 75% | 3012 fps | 99.8% |
| IMR 7977 Enduron | <<locked>> | 84% | 49,255 psi | 74% | 2887 fps | 95.1% |
| IMR 8133 Enduron | 80.6 gr | 80% | 33,649 psi | 50% | 2657 fps | 96.5% |
| Lovex D100 | <<locked>> | 90% | 53,751 psi | 81% | 2999 fps | 95.3% |
| Lovex S071 | <<locked>> | 80% | 44,802 psi | 67% | 2805 fps | 100% |
| Norma 217 | <<locked>> | 80% | 34,243 psi | 51% | 2684 fps | 98.7% |
| Norma MRP | <<locked>> | 80% | 56,101 psi | 84% | 3097 fps | 100% |
| Ramshot Grand | <<locked>> | 80% | 51,387 psi | 77% | 3031 fps | 100% |
| Ramshot LRT | <<locked>> | 94% | 55,593 psi | 83% | 3140 fps | 95.4% |
| Ramshot Magnum | <<locked>> | 80% | 46,412 psi | 70% | 2897 fps | 100% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 29,530 psi | 44% | 1847 fps | 100% |
| ReloadSwiss RS 76 | <<locked>> | 80% | 44,324 psi | 66% | 2946 fps | 100% |
| ReloadSwiss RS 80 | <<locked>> | 80% | 40,843 psi | 61% | 2841 fps | 97.7% |
| Rottweil R 904 | <<locked>> | 80% | 56,086 psi | 84% | 3038 fps | 100% |
| Rottweil R 905 | <<locked>> | 80% | 55,550 psi | 83% | 3051 fps | 100% |
| Shooters World 50 BMG | <<locked>> | 90% | 53,751 psi | 81% | 2999 fps | 95.3% |
| SNPE Vectan SP 13 | <<locked>> | 92% | 43,918 psi | 66% | 2851 fps | 95.8% |
| SNPE Vectan Tubal 8000 | <<locked>> | 80% | 55,201 psi | 83% | 3048 fps | 100% |
| Somchem S385 | <<locked>> | 80% | 55,883 psi | 84% | 3015 fps | 100% |
| Vihtavuori 20N29 | <<locked>> | 98% | 47,645 psi | 71% | 2940 fps | 95.2% |
| Vihtavuori N165 | <<locked>> | 80% | 49,226 psi | 74% | 2897 fps | 100% |
| Vihtavuori N170 | <<locked>> | 82% | 45,484 psi | 68% | 2854 fps | 95.7% |
| Vihtavuori N555 | <<locked>> | 80% | 55,912 psi | 84% | 3015 fps | 100% |
| Vihtavuori N560 | <<locked>> | 80% | 55,317 psi | 83% | 3107 fps | 100% |
| Vihtavuori N565 | <<locked>> | 80% | 46,499 psi | 70% | 2920 fps | 99.3% |
| Vihtavuori N568 | <<locked>> | 80% | 41,611 psi | 62% | 2854 fps | 97.4% |
| Vihtavuori N570 | 88.1 gr | 82% | 42,786 psi | 64% | 2917 fps | 95.9% |
| Winchester StaBALL HD | <<locked>> | 80% | 51,866 psi | 78% | 3022 fps | 100% |
| Winchester Supreme 780 | <<locked>> | 80% | 52,011 psi | 78% | 2956 fps | 100% |
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 56 powders for 7.21 Firebird loaded with the .284 | 158gr | Prvi Partizan Grom. Hodgdon Retumbo delivers the highest muzzle velocity at 3,232 fps; across all powders the maximum-charge window runs from 2,011 fps to 3,232 fps. Accurate 8700 gives the best case fill at 100 %, and 56 of the 56 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 158.0 gr projectile in 0.284" calls for a 1:11.0 twist; slower twists will usually not stabilise this weight. Accurate 8700, 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 2218, Vihtavuori N570, IMR 8133 Enduron rank at the top here: for 7.21 Firebird with the .284 | 158gr | Prvi Partizan Grom they combine a high case fill with complete burn and sit in the upper velocity band. As outliers, Hodgdon 50BMG 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.