Load Specifications
Load data in caliber 7.21 Firebird with .284 | 145gr | Speer Grand Slam bullet and 52 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are ADI AR 2218, Hodgdon Retumbo 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% | 57,406 psi | 86% | 3117 fps | 100% |
| Accurate 8700ᴾ | <<locked>> | 100% | 53,998 psi | 81% | 3156 fps | 98% |
| Accurate MAGPRO | <<locked>> | 82% | 56,608 psi | 85% | 3232 fps | 99.7% |
| ADI AR 2209 | <<locked>> | 82% | 58,015 psi | 87% | 3212 fps | 100% |
| ADI AR 2213 | <<locked>> | 84% | 57,043 psi | 86% | 3228 fps | 100% |
| ADI AR 2217 | <<locked>> | 92% | 57,043 psi | 86% | 3215 fps | 100% |
| ADI AR 2218 | <<locked>> | 96% | 58,030 psi | 87% | 3353 fps | 99.4% |
| ADI AR 2225 | <<locked>> | 94% | 57,072 psi | 86% | 3238 fps | 100% |
| Alliant Reloder-19 | <<locked>> | 82% | 57,653 psi | 86% | 3199 fps | 100% |
| Alliant Reloder-22 | <<locked>> | 84% | 57,638 psi | 86% | 3222 fps | 100% |
| Alliant Reloder-23 | <<locked>> | 86% | 59,756 psi | 90% | 3173 fps | 100% |
| Alliant Reloder-25 | <<locked>> | 88% | 57,072 psi | 86% | 3202 fps | 100% |
| Alliant Reloder-33 | <<locked>> | 94% | 60,321 psi | 90% | 3323 fps | 99.3% |
| Alliant Reloder-50 | <<locked>> | 96% | 56,507 psi | 85% | 3248 fps | 98.5% |
| Baschieri & Pellagri 109 | <<locked>> | 86% | 57,203 psi | 86% | 3186 fps | 99% |
| Bofors RP15 | <<locked>> | 86% | 57,203 psi | 86% | 3215 fps | 100% |
| Bofors RP30 | <<locked>> | 90% | 57,014 psi | 85% | 3228 fps | 100% |
| Bofors RP5 | <<locked>> | 84% | 57,638 psi | 86% | 3222 fps | 100% |
| Hodgdon H1000 | <<locked>> | 90% | 58,291 psi | 87% | 3232 fps | 100% |
| Hodgdon H4831 | <<locked>> | 84% | 59,437 psi | 89% | 3219 fps | 99.9% |
| Hodgdon H4831 SC | <<locked>> | 84% | 58,320 psi | 87% | 3202 fps | 99.9% |
| Hodgdon Retumbo | <<locked>> | 88% | 56,956 psi | 85% | 3304 fps | 100% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 37,985 psi | 57% | 2096 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 84% | 59,219 psi | 89% | 3192 fps | 100% |
| IMR 7828 SSC | <<locked>> | 86% | 59,857 psi | 90% | 3281 fps | 100% |
| IMR 7977 Enduron | <<locked>> | 90% | 58,088 psi | 87% | 3143 fps | 96.5% |
| IMR 8133 Enduron | <<locked>> | 98% | 59,843 psi | 90% | 3284 fps | 100% |
| Lovex D100 | <<locked>> | 94% | 60,104 psi | 90% | 3196 fps | 96% |
| Lovex S071 | <<locked>> | 90% | 59,625 psi | 89% | 3150 fps | 100% |
| Norma 217 | <<locked>> | 96% | 57,580 psi | 86% | 3245 fps | 100% |
| Norma MRP | <<locked>> | 82% | 57,928 psi | 87% | 3235 fps | 100% |
| Ramshot Grand | <<locked>> | 84% | 57,464 psi | 86% | 3241 fps | 100% |
| Ramshot Magnum | <<locked>> | 88% | 60,191 psi | 90% | 3222 fps | 100% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 39,044 psi | 59% | 2146 fps | 100% |
| ReloadSwiss RS 76 | <<locked>> | 88% | 58,102 psi | 87% | 3284 fps | 100% |
| ReloadSwiss RS 80 | <<locked>> | 90% | 57,203 psi | 86% | 3255 fps | 99.8% |
| Rottweil R 904 | <<locked>> | 82% | 58,189 psi | 87% | 3179 fps | 100% |
| Rottweil R 905 | <<locked>> | 82% | 57,522 psi | 86% | 3192 fps | 100% |
| Shooters World 50 BMG | <<locked>> | 94% | 60,104 psi | 90% | 3196 fps | 96% |
| SNPE Vectan SP 13ᴾ | <<locked>> | 100% | 55,637 psi | 83% | 3166 fps | 98% |
| SNPE Vectan Tubal 8000 | <<locked>> | 82% | 57,159 psi | 86% | 3186 fps | 100% |
| Somchem S361 | <<locked>> | 82% | 59,654 psi | 89% | 3163 fps | 100% |
| Somchem S385 | <<locked>> | 82% | 57,783 psi | 87% | 3153 fps | 100% |
| Vihtavuori N165 | <<locked>> | 86% | 58,088 psi | 87% | 3143 fps | 100% |
| Vihtavuori N170 | <<locked>> | 90% | 57,667 psi | 86% | 3176 fps | 97.8% |
| Vihtavuori N555 | <<locked>> | 82% | 57,638 psi | 86% | 3153 fps | 100% |
| Vihtavuori N560 | <<locked>> | 82% | 57,116 psi | 86% | 3245 fps | 99.9% |
| Vihtavuori N565 | <<locked>> | 88% | 58,885 psi | 88% | 3241 fps | 100% |
| Vihtavuori N568 | <<locked>> | 90% | 57,377 psi | 86% | 3261 fps | 99.7% |
| Vihtavuori N570 | <<locked>> | 92% | 58,914 psi | 88% | 3330 fps | 98.9% |
| Winchester StaBALL HD | <<locked>> | 84% | 57,580 psi | 86% | 3219 fps | 100% |
| Winchester Supreme 780 | <<locked>> | 84% | 57,711 psi | 87% | 3153 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% | 50,198 psi | 75% | 3005 fps | 100% |
| Accurate 8700 | <<locked>> | 94% | 43,076 psi | 65% | 2943 fps | 95.1% |
| Accurate MAGPRO | <<locked>> | 80% | 52,794 psi | 79% | 3166 fps | 99.3% |
| ADI AR 2209 | <<locked>> | 80% | 54,244 psi | 81% | 3150 fps | 100% |
| ADI AR 2213 | <<locked>> | 80% | 49,647 psi | 74% | 3097 fps | 99.5% |
| ADI AR 2217 | <<locked>> | 80% | 37,115 psi | 56% | 2818 fps | 97.2% |
| ADI AR 2218 | 98.9 gr | 88% | 42,975 psi | 64% | 3035 fps | 95.6% |
| ADI AR 2225 | <<locked>> | 80% | 34,519 psi | 52% | 2792 fps | 99% |
| Alliant Reloder-19 | <<locked>> | 80% | 54,041 psi | 81% | 3136 fps | 100% |
| Alliant Reloder-22 | <<locked>> | 80% | 50,430 psi | 76% | 3100 fps | 99.9% |
| Alliant Reloder-23 | <<locked>> | 80% | 49,008 psi | 73% | 3012 fps | 100% |
| Alliant Reloder-25 | <<locked>> | 80% | 43,250 psi | 65% | 2966 fps | 100% |
| Alliant Reloder-33 | <<locked>> | 86% | 44,686 psi | 67% | 3028 fps | 96.1% |
| Alliant Reloder-50 | <<locked>> | 90% | 45,005 psi | 67% | 3018 fps | 95.6% |
| Baschieri & Pellagri 109 | <<locked>> | 80% | 46,862 psi | 70% | 2992 fps | 97.1% |
| Bofors RP15 | <<locked>> | 80% | 46,818 psi | 70% | 3028 fps | 99.6% |
| Bofors RP30 | <<locked>> | 80% | 40,466 psi | 61% | 2904 fps | 98.2% |
| Bofors RP5 | <<locked>> | 80% | 50,430 psi | 76% | 3100 fps | 99.9% |
| Hodgdon H1000 | <<locked>> | 80% | 40,567 psi | 61% | 2904 fps | 98.7% |
| Hodgdon H4831 | <<locked>> | 80% | 51,822 psi | 78% | 3087 fps | 99.4% |
| Hodgdon H4831 SC | <<locked>> | 80% | 50,995 psi | 76% | 3074 fps | 99.3% |
| Hodgdon Retumbo | 84.8 gr | 80% | 42,395 psi | 64% | 3031 fps | 99.7% |
| Hodgdon TrailBoss | <<locked>> | 80% | 28,543 psi | 43% | 1880 fps | 100% |
| IMR 4955 Enduron | <<locked>> | 80% | 52,083 psi | 78% | 3071 fps | 99.5% |
| IMR 7828 SSC | <<locked>> | 80% | 48,399 psi | 73% | 3081 fps | 99.4% |
| IMR 7977 Enduron | <<locked>> | 88% | 54,418 psi | 82% | 3077 fps | 95.7% |
| IMR 8133 Enduron | <<locked>> | 82% | 34,476 psi | 52% | 2766 fps | 95.9% |
| Lovex D100 | <<locked>> | 92% | 55,869 psi | 84% | 3127 fps | 95% |
| Lovex S071 | <<locked>> | 80% | 43,250 psi | 65% | 2874 fps | 100% |
| Norma 217 | <<locked>> | 80% | 32,663 psi | 49% | 2730 fps | 97.4% |
| Norma MRP | <<locked>> | 80% | 53,998 psi | 81% | 3173 fps | 100% |
| Ramshot Grand | <<locked>> | 80% | 49,385 psi | 74% | 3100 fps | 99.7% |
| Ramshot Magnum | <<locked>> | 80% | 44,585 psi | 67% | 2959 fps | 99.8% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 29,428 psi | 44% | 1926 fps | 100% |
| ReloadSwiss RS 76 | <<locked>> | 80% | 42,380 psi | 64% | 3009 fps | 100% |
| ReloadSwiss RS 80 | <<locked>> | 80% | 38,943 psi | 58% | 2887 fps | 96.3% |
| Rottweil R 904 | <<locked>> | 80% | 54,534 psi | 82% | 3117 fps | 99.9% |
| Rottweil R 905 | <<locked>> | 80% | 53,809 psi | 81% | 3130 fps | 100% |
| Shooters World 50 BMG | <<locked>> | 92% | 55,869 psi | 84% | 3127 fps | 95% |
| SNPE Vectan SP 13 | <<locked>> | 94% | 45,237 psi | 68% | 2966 fps | 95.3% |
| SNPE Vectan Tubal 8000 | <<locked>> | 80% | 53,461 psi | 80% | 3123 fps | 100% |
| Somchem S361 | <<locked>> | 80% | 55,869 psi | 84% | 3104 fps | 99.8% |
| Somchem S385 | <<locked>> | 80% | 54,143 psi | 81% | 3097 fps | 100% |
| Vihtavuori N165 | <<locked>> | 80% | 47,630 psi | 71% | 2969 fps | 99.9% |
| Vihtavuori N170 | <<locked>> | 84% | 47,036 psi | 71% | 2979 fps | 95.3% |
| Vihtavuori N555 | <<locked>> | 80% | 53,940 psi | 81% | 3097 fps | 100% |
| Vihtavuori N560 | <<locked>> | 80% | 53,287 psi | 80% | 3176 fps | 99.6% |
| Vihtavuori N565 | <<locked>> | 80% | 44,846 psi | 67% | 2982 fps | 98.6% |
| Vihtavuori N568 | <<locked>> | 80% | 39,914 psi | 60% | 2907 fps | 96% |
| Vihtavuori N570 | 92.4 gr | 84% | 44,034 psi | 66% | 3038 fps | 95.3% |
| Winchester StaBALL HD | <<locked>> | 80% | 49,501 psi | 74% | 3094 fps | 100% |
| Winchester Supreme 780 | <<locked>> | 80% | 50,285 psi | 75% | 3028 fps | 99.9% |
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 | 145gr | Speer Grand Slam. ADI AR 2218 delivers the highest muzzle velocity at 3,353 fps; across all powders the maximum-charge window runs from 2,096 fps to 3,353 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 145.0 gr projectile in 0.284" calls for a 1:13.0 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. ADI AR 2218, Hodgdon Retumbo, Vihtavuori N570 rank at the top here: for 7.21 Firebird with the .284 | 145gr | Speer Grand Slam they combine a high case fill with complete burn and sit in the upper velocity band. As outliers, Hodgdon 50BMG, 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.