Load Specifications
Load data in caliber 7.21 Firebird with .284 | 135gr | Atomic 29 HP bullet and 52 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 ReloadSwiss RS 76.
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>> | 86% | 57,537 psi | 86% | 3212 fps | 100% |
| Accurate 8700ᴾ | <<locked>> | 100% | 49,385 psi | 74% | 3153 fps | 96.2% |
| Accurate MAGPRO | <<locked>> | 84% | 56,681 psi | 85% | 3323 fps | 99.4% |
| ADI AR 2209 | <<locked>> | 84% | 58,291 psi | 87% | 3307 fps | 100% |
| ADI AR 2213 | <<locked>> | 86% | 57,305 psi | 86% | 3327 fps | 99.8% |
| ADI AR 2217 | <<locked>> | 94% | 56,579 psi | 85% | 3297 fps | 100% |
| ADI AR 2218 | <<locked>> | 98% | 57,682 psi | 86% | 3428 fps | 98.8% |
| ADI AR 2225 | <<locked>> | 96% | 56,217 psi | 84% | 3320 fps | 100% |
| Alliant Reloder-19 | <<locked>> | 84% | 57,899 psi | 87% | 3294 fps | 100% |
| Alliant Reloder-22 | <<locked>> | 86% | 57,827 psi | 87% | 3320 fps | 100% |
| Alliant Reloder-23 | <<locked>> | 88% | 59,770 psi | 90% | 3274 fps | 100% |
| Alliant Reloder-25 | <<locked>> | 90% | 56,681 psi | 85% | 3294 fps | 100% |
| Alliant Reloder-26 | <<locked>> | 82% | 56,753 psi | 85% | 3307 fps | 100% |
| Alliant Reloder-33 | <<locked>> | 96% | 59,828 psi | 90% | 3406 fps | 98.8% |
| Alliant Reloder-50ᴾ | <<locked>> | 100% | 60,118 psi | 90% | 3396 fps | 98.5% |
| Baschieri & Pellagri 109 | <<locked>> | 88% | 57,537 psi | 86% | 3274 fps | 98.6% |
| Bofors RP15 | <<locked>> | 88% | 57,203 psi | 86% | 3307 fps | 100% |
| Bofors RP30 | <<locked>> | 92% | 56,594 psi | 85% | 3314 fps | 99.9% |
| Bofors RP5 | <<locked>> | 86% | 57,827 psi | 87% | 3320 fps | 100% |
| Hodgdon H1000 | <<locked>> | 92% | 58,247 psi | 87% | 3323 fps | 100% |
| Hodgdon H4831 | <<locked>> | 86% | 60,002 psi | 90% | 3317 fps | 99.8% |
| Hodgdon H4831 SC | <<locked>> | 86% | 58,827 psi | 88% | 3297 fps | 99.7% |
| Hodgdon Hybrid 100V | <<locked>> | 82% | 58,523 psi | 88% | 3202 fps | 100% |
| Hodgdon Retumbo | <<locked>> | 92% | 60,350 psi | 90% | 3458 fps | 100% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 37,855 psi | 57% | 2156 fps | 100% |
| IMR 4350 | <<locked>> | 82% | 60,162 psi | 90% | 3274 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 86% | 59,727 psi | 90% | 3287 fps | 99.8% |
| IMR 7828 SSC | <<locked>> | 88% | 59,857 psi | 90% | 3373 fps | 100% |
| IMR 8133 Enduronᴾ | <<locked>> | 100% | 59,161 psi | 89% | 3366 fps | 100% |
| Lovex S071 | <<locked>> | 92% | 59,422 psi | 89% | 3238 fps | 100% |
| Norma 217 | <<locked>> | 98% | 56,652 psi | 85% | 3323 fps | 100% |
| Norma MRP | <<locked>> | 84% | 58,001 psi | 87% | 3333 fps | 100% |
| Ramshot Grand | <<locked>> | 86% | 57,261 psi | 86% | 3330 fps | 99.9% |
| Ramshot Magnum | <<locked>> | 90% | 60,205 psi | 90% | 3314 fps | 100% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 38,885 psi | 58% | 2208 fps | 100% |
| ReloadSwiss RS 76 | <<locked>> | 90% | 57,508 psi | 86% | 3376 fps | 100% |
| ReloadSwiss RS 80 | <<locked>> | 92% | 56,623 psi | 85% | 3333 fps | 99.5% |
| Rottweil R 904 | <<locked>> | 84% | 58,639 psi | 88% | 3274 fps | 99.9% |
| Rottweil R 905 | <<locked>> | 84% | 57,885 psi | 87% | 3287 fps | 100% |
| SNPE Vectan SP 13ᴾ | <<locked>> | 100% | 51,445 psi | 77% | 3169 fps | 96.3% |
| SNPE Vectan Tubal 8000 | <<locked>> | 84% | 57,508 psi | 86% | 3284 fps | 100% |
| Somchem S361 | <<locked>> | 84% | 60,307 psi | 90% | 3258 fps | 99.8% |
| Somchem S385 | <<locked>> | 84% | 58,160 psi | 87% | 3251 fps | 100% |
| Vihtavuori N165 | <<locked>> | 88% | 58,349 psi | 87% | 3238 fps | 100% |
| Vihtavuori N170 | <<locked>> | 92% | 57,928 psi | 87% | 3261 fps | 97.1% |
| Vihtavuori N555 | <<locked>> | 84% | 57,580 psi | 86% | 3248 fps | 100% |
| Vihtavuori N560 | <<locked>> | 84% | 57,261 psi | 86% | 3337 fps | 99.7% |
| Vihtavuori N565 | <<locked>> | 90% | 58,813 psi | 88% | 3330 fps | 99.9% |
| Vihtavuori N568 | <<locked>> | 92% | 56,927 psi | 85% | 3340 fps | 99.3% |
| Vihtavuori N570 | <<locked>> | 94% | 58,349 psi | 87% | 3409 fps | 98.2% |
| Winchester StaBALL HD | <<locked>> | 86% | 56,927 psi | 85% | 3310 fps | 100% |
| Winchester Supreme 780 | <<locked>> | 86% | 58,044 psi | 87% | 3248 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% | 46,963 psi | 70% | 3035 fps | 100% |
| Accurate 8700 | <<locked>> | 98% | 45,890 psi | 69% | 3081 fps | 95.1% |
| Accurate MAGPRO | <<locked>> | 80% | 49,139 psi | 74% | 3182 fps | 98.2% |
| ADI AR 2209 | <<locked>> | 80% | 50,937 psi | 76% | 3179 fps | 99.7% |
| ADI AR 2213 | <<locked>> | 80% | 46,311 psi | 69% | 3120 fps | 98.5% |
| ADI AR 2217 | <<locked>> | 80% | 34,519 psi | 52% | 2825 fps | 95.2% |
| ADI AR 2218 | 101.8 gr | 92% | 46,035 psi | 69% | 3186 fps | 95.7% |
| ADI AR 2225 | <<locked>> | 80% | 31,850 psi | 48% | 2789 fps | 97.2% |
| Alliant Reloder-19 | <<locked>> | 80% | 50,850 psi | 76% | 3169 fps | 99.7% |
| Alliant Reloder-22 | <<locked>> | 80% | 47,094 psi | 71% | 3120 fps | 99.4% |
| Alliant Reloder-23 | <<locked>> | 80% | 45,803 psi | 69% | 3048 fps | 100% |
| Alliant Reloder-25 | <<locked>> | 80% | 39,914 psi | 60% | 2986 fps | 99.9% |
| Alliant Reloder-26 | <<locked>> | 80% | 52,707 psi | 79% | 3241 fps | 100% |
| Alliant Reloder-33 | <<locked>> | 88% | 44,092 psi | 66% | 3097 fps | 95% |
| Alliant Reloder-50 | <<locked>> | 94% | 47,921 psi | 72% | 3166 fps | 95.7% |
| Baschieri & Pellagri 109 | <<locked>> | 80% | 44,208 psi | 66% | 3012 fps | 95.4% |
| Bofors RP15 | <<locked>> | 80% | 43,816 psi | 66% | 3051 fps | 98.8% |
| Bofors RP30 | <<locked>> | 80% | 37,362 psi | 56% | 2913 fps | 96.4% |
| Bofors RP5 | <<locked>> | 80% | 47,094 psi | 71% | 3120 fps | 99.4% |
| Hodgdon H1000 | <<locked>> | 80% | 37,623 psi | 56% | 2913 fps | 97.2% |
| Hodgdon H4831 | <<locked>> | 80% | 48,718 psi | 73% | 3117 fps | 98.5% |
| Hodgdon H4831 SC | <<locked>> | 80% | 47,906 psi | 72% | 3097 fps | 98.3% |
| Hodgdon Hybrid 100V | <<locked>> | 80% | 54,853 psi | 82% | 3150 fps | 100% |
| Hodgdon Retumbo | 83.5 gr | 80% | 38,986 psi | 58% | 3038 fps | 98.6% |
| Hodgdon TrailBoss | <<locked>> | 80% | 28,427 psi | 43% | 1936 fps | 100% |
| IMR 4350 | <<locked>> | 80% | 56,391 psi | 85% | 3215 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 80% | 49,284 psi | 74% | 3100 fps | 98.7% |
| IMR 7828 SSC | <<locked>> | 80% | 45,005 psi | 67% | 3097 fps | 98.3% |
| IMR 8133 Enduron | <<locked>> | 86% | 36,463 psi | 55% | 2900 fps | 95.9% |
| Lovex S071 | <<locked>> | 80% | 40,466 psi | 61% | 2900 fps | 99.7% |
| Norma 217 | <<locked>> | 80% | 29,675 psi | 44% | 2723 fps | 95% |
| Norma MRP | <<locked>> | 80% | 50,343 psi | 75% | 3202 fps | 100% |
| Ramshot Grand | <<locked>> | 80% | 45,687 psi | 68% | 3117 fps | 98.7% |
| Ramshot Magnum | <<locked>> | 80% | 41,234 psi | 62% | 2976 fps | 99.1% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 29,138 psi | 44% | 1982 fps | 100% |
| ReloadSwiss RS 76 | 89.4 gr | 80% | 38,711 psi | 58% | 3009 fps | 99.4% |
| ReloadSwiss RS 80 | <<locked>> | 82% | 38,566 psi | 58% | 2959 fps | 95.2% |
| Rottweil R 904 | <<locked>> | 80% | 51,459 psi | 77% | 3150 fps | 99.3% |
| Rottweil R 905 | <<locked>> | 80% | 50,473 psi | 76% | 3159 fps | 99.8% |
| SNPE Vectan SP 13 | <<locked>> | 98% | 48,008 psi | 72% | 3100 fps | 95.3% |
| SNPE Vectan Tubal 8000 | <<locked>> | 80% | 50,125 psi | 75% | 3153 fps | 99.7% |
| Somchem S361 | <<locked>> | 80% | 52,736 psi | 79% | 3133 fps | 99.1% |
| Somchem S385 | <<locked>> | 80% | 50,952 psi | 76% | 3130 fps | 100% |
| Vihtavuori N165 | <<locked>> | 80% | 44,657 psi | 67% | 2995 fps | 99.4% |
| Vihtavuori N170 | <<locked>> | 88% | 50,430 psi | 76% | 3123 fps | 95.4% |
| Vihtavuori N555 | <<locked>> | 80% | 50,459 psi | 76% | 3133 fps | 100% |
| Vihtavuori N560 | <<locked>> | 80% | 49,792 psi | 75% | 3199 fps | 98.8% |
| Vihtavuori N565 | <<locked>> | 80% | 41,553 psi | 62% | 2992 fps | 97.1% |
| Vihtavuori N568 | <<locked>> | 84% | 42,540 psi | 64% | 3051 fps | 96.1% |
| Vihtavuori N570 | <<locked>> | 88% | 46,833 psi | 70% | 3186 fps | 95.4% |
| Winchester StaBALL HD | <<locked>> | 80% | 45,237 psi | 68% | 3120 fps | 100% |
| Winchester Supreme 780 | <<locked>> | 80% | 47,181 psi | 71% | 3054 fps | 99.4% |
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 59 powders for 7.21 Firebird loaded with the .284 | 135gr | Atomic 29 HP. Hodgdon Retumbo delivers the highest muzzle velocity at 3,458 fps; across all powders the maximum-charge window runs from 2,156 fps to 3,458 fps. Accurate 8700 gives the best case fill at 100 %, and 59 of the 59 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 135.0 gr projectile in 0.284" calls for a 1:11.0 twist; slower twists will usually not stabilise this weight. Accurate 8700, Alliant Reloder-50, Hodgdon TrailBoss 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, ReloadSwiss RS 76 rank at the top here: for 7.21 Firebird with the .284 | 135gr | Atomic 29 HP they combine a high case fill with complete burn and sit in the upper velocity band. As outliers, Hodgdon US 869, Ramshot LRT, Vihtavuori 20N29 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.