Load Specifications
Load data in caliber .338 RCM with .338 | 225gr | Sierra Pro-Hunter bullet and 96 powders. The key underlying parameters are shown in the table above. The recommended powders for this cartridge and bullet combination are Alliant Power Pro 2000-MR, ReloadSwiss RS 52 and Hodgdon CFE223.
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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You can find more information in our FAQ: How can I use the Personalized Load Calculator?
Max Load - Barrel Length: 24"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| Accurate 2015 | <<locked>> | 90% | 55,288 psi | 89% | 2467 fps | 100% |
| Accurate 2200 | <<locked>> | 82% | 55,463 psi | 89% | 2556 fps | 99.3% |
| Accurate 2460 | <<locked>> | 86% | 53,650 psi | 86% | 2493 fps | 100% |
| Accurate 2495 | <<locked>> | 96% | 55,608 psi | 89% | 2523 fps | 100% |
| Accurate 2520 | <<locked>> | 90% | 54,839 psi | 88% | 2543 fps | 100% |
| Accurate 4064 | <<locked>> | 98% | 55,187 psi | 88% | 2559 fps | 100% |
| Accurate 4350ᴾ | <<locked>> | 100% | 43,859 psi | 70% | 2470 fps | 97.3% |
| Accurate LT-30 | <<locked>> | 84% | 55,303 psi | 89% | 2418 fps | 100% |
| Accurate LT-32 | <<locked>> | 84% | 55,709 psi | 89% | 2441 fps | 100% |
| ADI AR 2206H | <<locked>> | 92% | 53,925 psi | 86% | 2549 fps | 99.6% |
| ADI AR 2208 | <<locked>> | 98% | 54,940 psi | 88% | 2546 fps | 99.3% |
| ADI AR 2219 | <<locked>> | 84% | 55,637 psi | 89% | 2530 fps | 100% |
| ADI Benchmark 8208 | <<locked>> | 90% | 53,374 psi | 86% | 2510 fps | 99.9% |
| Alliant AR-Comp | <<locked>> | 90% | 52,910 psi | 85% | 2493 fps | 100% |
| Alliant Power Pro 1200-R | <<locked>> | 86% | 54,911 psi | 88% | 2605 fps | 99.9% |
| Alliant Power Pro 2000-MR | <<locked>> | 94% | 53,476 psi | 86% | 2651 fps | 99.2% |
| Alliant Reloder- TS 15.5 | <<locked>> | 98% | 54,012 psi | 87% | 2562 fps | 99.9% |
| Alliant Reloder-10x | <<locked>> | 86% | 55,056 psi | 88% | 2470 fps | 100% |
| Alliant Reloder-15 | <<locked>> | 96% | 55,027 psi | 88% | 2585 fps | 99.4% |
| Alliant Reloder-16ᴾ | <<locked>> | 100% | 44,237 psi | 71% | 2474 fps | 97.4% |
| Alliant Reloder-17ᴾ | <<locked>> | 100% | 50,981 psi | 82% | 2618 fps | 99.7% |
| Baschieri & Pellagri 106 | <<locked>> | 84% | 54,360 psi | 87% | 2421 fps | 100% |
| Baschieri & Pellagri 107 | <<locked>> | 92% | 53,548 psi | 86% | 2562 fps | 98.9% |
| Bofors RP3 | <<locked>> | 98% | 54,404 psi | 87% | 2579 fps | 99.9% |
| Hodgdon Benchmark | <<locked>> | 90% | 55,825 psi | 90% | 2500 fps | 100% |
| Hodgdon BL-C2 | <<locked>> | 92% | 55,666 psi | 89% | 2585 fps | 100% |
| Hodgdon CFE223 | <<locked>> | 88% | 53,592 psi | 86% | 2621 fps | 99.4% |
| Hodgdon H322 | <<locked>> | 86% | 54,331 psi | 87% | 2513 fps | 100% |
| Hodgdon H335 | <<locked>> | 86% | 55,361 psi | 89% | 2539 fps | 100% |
| Hodgdon H380 | <<locked>> | 98% | 56,159 psi | 90% | 2589 fps | 98.7% |
| Hodgdon H4895 | <<locked>> | 92% | 54,360 psi | 87% | 2559 fps | 99.8% |
| Hodgdon Hybrid 100Vᴾ | <<locked>> | 100% | 40,553 psi | 65% | 2375 fps | 98% |
| Hodgdon LEVERevolution | <<locked>> | 96% | 56,347 psi | 90% | 2631 fps | 100% |
| Hodgdon TrailBossᴾ | <<locked>> | 100% | 34,679 psi | 56% | 1499 fps | 100% |
| Hodgdon VARGET | <<locked>> | 94% | 56,057 psi | 90% | 2562 fps | 99.9% |
| IMR 3031 | <<locked>> | 92% | 53,490 psi | 86% | 2546 fps | 100% |
| IMR 4064 | <<locked>> | 96% | 54,433 psi | 87% | 2530 fps | 99.4% |
| IMR 4166 Enduron | <<locked>> | 94% | 55,579 psi | 89% | 2513 fps | 96.6% |
| IMR 4198 | <<locked>> | 86% | 55,651 psi | 89% | 2434 fps | 100% |
| IMR 4451 Enduronᴾ | <<locked>> | 100% | 54,128 psi | 87% | 2523 fps | 96.2% |
| IMR 4831ᴾ | <<locked>> | 100% | 42,076 psi | 67% | 2421 fps | 96.9% |
| IMR 4895 | <<locked>> | 96% | 56,434 psi | 90% | 2615 fps | 99.8% |
| IMR 8208 XBR | <<locked>> | 90% | 53,374 psi | 86% | 2510 fps | 99.9% |
| Lovex D073.5 | <<locked>> | 86% | 53,548 psi | 86% | 2503 fps | 100% |
| Lovex D073.6 | <<locked>> | 94% | 56,376 psi | 90% | 2572 fps | 100% |
| Lovex S060 | <<locked>> | 92% | 54,621 psi | 88% | 2490 fps | 99.6% |
| Lovex S062 | <<locked>> | 96% | 53,751 psi | 86% | 2526 fps | 100% |
| Lovex S065ᴾ | <<locked>> | 100% | 49,603 psi | 80% | 2470 fps | 96.9% |
| Norma 200 | <<locked>> | 82% | 55,056 psi | 88% | 2448 fps | 100% |
| Norma 201 | <<locked>> | 94% | 56,144 psi | 90% | 2546 fps | 100% |
| Norma 202 | <<locked>> | 92% | 53,098 psi | 85% | 2507 fps | 100% |
| Norma 203B | <<locked>> | 96% | 54,128 psi | 87% | 2572 fps | 99.6% |
| Norma URPᴾ | <<locked>> | 100% | 44,280 psi | 71% | 2467 fps | 97.2% |
| Ramshot Big Game | <<locked>> | 96% | 54,230 psi | 87% | 2595 fps | 99.5% |
| Ramshot TAC | <<locked>> | 90% | 53,896 psi | 86% | 2523 fps | 97.9% |
| Ramshot Wild Boar | <<locked>> | 92% | 56,420 psi | 90% | 2589 fps | 99.7% |
| Ramshot X-Terminator | <<locked>> | 88% | 54,824 psi | 88% | 2513 fps | 99.5% |
| ReloadSwiss RS 14ᴾ | <<locked>> | 100% | 34,824 psi | 56% | 1532 fps | 100% |
| ReloadSwiss RS 40 | <<locked>> | 86% | 53,403 psi | 86% | 2500 fps | 100% |
| ReloadSwiss RS 50 | <<locked>> | 96% | 53,258 psi | 85% | 2523 fps | 96.9% |
| ReloadSwiss RS 52 | <<locked>> | 94% | 54,810 psi | 88% | 2644 fps | 99.4% |
| ReloadSwiss RS 60ᴾ | <<locked>> | 100% | 54,476 psi | 87% | 2674 fps | 100% |
| ReloadSwiss RS 62ᴾ | <<locked>> | 100% | 43,685 psi | 70% | 2487 fps | 96.8% |
| ReloadSwiss RS 70ᴾ | <<locked>> | 100% | 45,194 psi | 72% | 2503 fps | 96.1% |
| Rottweil R 901 | <<locked>> | 90% | 53,925 psi | 86% | 2487 fps | 100% |
| Rottweil R 902 | <<locked>> | 94% | 53,214 psi | 85% | 2500 fps | 99.9% |
| Rottweil R 903ᴾ | <<locked>> | 100% | 53,940 psi | 86% | 2566 fps | 99.8% |
| Shooters World Long Rifleᴾ | <<locked>> | 100% | 49,603 psi | 80% | 2470 fps | 96.9% |
| Shooters World Match Rifle | <<locked>> | 94% | 56,376 psi | 90% | 2572 fps | 100% |
| Shooters World Precision | <<locked>> | 96% | 53,751 psi | 86% | 2526 fps | 100% |
| Shooters World Tactical Rifle | <<locked>> | 84% | 53,374 psi | 86% | 2474 fps | 99.8% |
| SNPE Vectan BA6 1/2 | <<locked>> | 82% | 56,014 psi | 90% | 2192 fps | 100% |
| SNPE Vectan SP 10 | <<locked>> | 84% | 56,014 psi | 90% | 2539 fps | 100% |
| SNPE Vectan SP 11ᴾ | <<locked>> | 100% | 55,883 psi | 90% | 2625 fps | 99.7% |
| SNPE Vectan SP 3 | <<locked>> | 86% | 56,043 psi | 90% | 2490 fps | 100% |
| SNPE Vectan SP 7 | <<locked>> | 92% | 55,622 psi | 89% | 2549 fps | 98.5% |
| SNPE Vectan SP 9 | <<locked>> | 94% | 55,999 psi | 90% | 2572 fps | 99.7% |
| SNPE Vectan Tubal 3000 | <<locked>> | 92% | 55,259 psi | 89% | 2454 fps | 100% |
| SNPE Vectan Tubal 5000 | <<locked>> | 98% | 54,476 psi | 87% | 2448 fps | 100% |
| Somchem S321 | <<locked>> | 88% | 54,505 psi | 87% | 2543 fps | 100% |
| Somchem S335 | <<locked>> | 92% | 53,954 psi | 87% | 2451 fps | 100% |
| Somchem S341 | <<locked>> | 92% | 54,781 psi | 88% | 2543 fps | 99.6% |
| Somchem S355ᴾ | <<locked>> | 100% | 54,694 psi | 88% | 2566 fps | 99.8% |
| Somchem S365ᴾ | <<locked>> | 100% | 39,349 psi | 63% | 2421 fps | 99% |
| Vihtavuori N130 | <<locked>> | 88% | 55,158 psi | 88% | 2428 fps | 100% |
| Vihtavuori N133 | <<locked>> | 92% | 55,100 psi | 88% | 2441 fps | 100% |
| Vihtavuori N135 | <<locked>> | 96% | 55,521 psi | 89% | 2513 fps | 100% |
| Vihtavuori N140 | <<locked>> | 94% | 53,621 psi | 86% | 2490 fps | 100% |
| Vihtavuori N150ᴾ | <<locked>> | 100% | 52,823 psi | 85% | 2507 fps | 100% |
| Vihtavuori N160ᴾ | <<locked>> | 100% | 46,673 psi | 75% | 2467 fps | 97.5% |
| Vihtavuori N530 | <<locked>> | 90% | 54,056 psi | 87% | 2513 fps | 100% |
| Vihtavuori N540 | <<locked>> | 96% | 55,027 psi | 88% | 2530 fps | 100% |
| Vihtavuori N550ᴾ | <<locked>> | 100% | 45,614 psi | 73% | 2474 fps | 97.2% |
| Winchester 6.5 StaBALLᴾ | <<locked>> | 100% | 47,921 psi | 77% | 2461 fps | 99.3% |
| Winchester 748 | <<locked>> | 90% | 53,098 psi | 85% | 2556 fps | 100% |
| Winchester StaBALL Match | <<locked>> | 94% | 55,492 psi | 89% | 2579 fps | 99.9% |
Recommended = one of the top powders for this cartridge and bullet combination.
Start Load - Barrel Length: 24"
| Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
| Accurate 2015 | <<locked>> | 80% | 40,669 psi | 65% | 2267 fps | 100% |
| Accurate 2200 | <<locked>> | 80% | 52,025 psi | 83% | 2507 fps | 98.9% |
| Accurate 2460 | <<locked>> | 80% | 43,903 psi | 70% | 2356 fps | 100% |
| Accurate 2495 | <<locked>> | 80% | 32,967 psi | 53% | 2188 fps | 100% |
| Accurate 2520 | <<locked>> | 80% | 39,131 psi | 63% | 2313 fps | 99.6% |
| Accurate 4064 | <<locked>> | 80% | 31,227 psi | 50% | 2172 fps | 98.9% |
| Accurate 4350 | <<locked>> | 96% | 38,189 psi | 61% | 2372 fps | 95.8% |
| Accurate LT-30 | <<locked>> | 80% | 49,139 psi | 79% | 2339 fps | 100% |
| Accurate LT-32 | <<locked>> | 80% | 49,472 psi | 79% | 2359 fps | 100% |
| ADI AR 2206H | <<locked>> | 80% | 37,231 psi | 60% | 2270 fps | 96.8% |
| ADI AR 2208 | <<locked>> | 84% | 36,027 psi | 58% | 2231 fps | 95.6% |
| ADI AR 2219 | <<locked>> | 80% | 48,617 psi | 78% | 2438 fps | 100% |
| ADI Benchmark 8208 | <<locked>> | 80% | 39,218 psi | 63% | 2287 fps | 98.4% |
| Alliant AR-Comp | <<locked>> | 80% | 38,145 psi | 61% | 2290 fps | 100% |
| Alliant Power Pro 1200-R | <<locked>> | 80% | 45,223 psi | 73% | 2457 fps | 99.1% |
| Alliant Power Pro 2000-MR | 49.6 gr | 84% | 38,305 psi | 61% | 2379 fps | 95.8% |
| Alliant Reloder- TS 15.5 | <<locked>> | 80% | 30,690 psi | 49% | 2156 fps | 95.7% |
| Alliant Reloder-10x | <<locked>> | 80% | 46,035 psi | 74% | 2352 fps | 100% |
| Alliant Reloder-15 | <<locked>> | 82% | 35,375 psi | 57% | 2254 fps | 95.6% |
| Alliant Reloder-16 | <<locked>> | 94% | 37,043 psi | 59% | 2333 fps | 95% |
| Alliant Reloder-17 | <<locked>> | 86% | 32,387 psi | 52% | 2257 fps | 95.2% |
| Baschieri & Pellagri 106 | <<locked>> | 80% | 47,834 psi | 77% | 2339 fps | 100% |
| Baschieri & Pellagri 107 | <<locked>> | 80% | 36,085 psi | 58% | 2267 fps | 95.1% |
| Bofors RP3 | <<locked>> | 80% | 29,921 psi | 48% | 2152 fps | 95.5% |
| Hodgdon Benchmark | <<locked>> | 80% | 41,249 psi | 66% | 2283 fps | 99.1% |
| Hodgdon BL-C2 | <<locked>> | 80% | 37,144 psi | 60% | 2297 fps | 98.5% |
| Hodgdon CFE223 | 48.3 gr | 80% | 40,727 psi | 65% | 2411 fps | 97.2% |
| Hodgdon H322 | <<locked>> | 80% | 44,744 psi | 72% | 2382 fps | 100% |
| Hodgdon H335 | <<locked>> | 80% | 45,136 psi | 72% | 2398 fps | 100% |
| Hodgdon H380 | <<locked>> | 88% | 40,422 psi | 65% | 2346 fps | 95.7% |
| Hodgdon H4895 | <<locked>> | 80% | 37,449 psi | 60% | 2283 fps | 97.4% |
| Hodgdon Hybrid 100V | <<locked>> | 92% | 31,720 psi | 51% | 2192 fps | 95.1% |
| Hodgdon LEVERevolution | <<locked>> | 80% | 33,460 psi | 54% | 2247 fps | 96.7% |
| Hodgdon TrailBoss | <<locked>> | 80% | 25,599 psi | 41% | 1335 fps | 100% |
| Hodgdon VARGET | <<locked>> | 80% | 36,216 psi | 58% | 2244 fps | 97% |
| IMR 3031 | <<locked>> | 80% | 36,260 psi | 58% | 2287 fps | 100% |
| IMR 4064 | <<locked>> | 82% | 35,462 psi | 57% | 2215 fps | 95.7% |
| IMR 4166 Enduron | <<locked>> | 90% | 48,892 psi | 78% | 2415 fps | 95.2% |
| IMR 4198 | <<locked>> | 80% | 46,702 psi | 75% | 2320 fps | 100% |
| IMR 4451 Enduron | <<locked>> | 98% | 50,908 psi | 82% | 2477 fps | 95.5% |
| IMR 4831 | <<locked>> | 96% | 36,985 psi | 59% | 2326 fps | 95.4% |
| IMR 4895 | <<locked>> | 80% | 33,924 psi | 54% | 2234 fps | 95.9% |
| IMR 8208 XBR | <<locked>> | 80% | 39,218 psi | 63% | 2287 fps | 98.4% |
| Lovex D073.5 | <<locked>> | 80% | 43,627 psi | 70% | 2359 fps | 99.6% |
| Lovex D073.6 | <<locked>> | 80% | 35,520 psi | 57% | 2257 fps | 99% |
| Lovex S060 | <<locked>> | 80% | 38,101 psi | 61% | 2224 fps | 97% |
| Lovex S062 | <<locked>> | 80% | 32,953 psi | 53% | 2175 fps | 96.9% |
| Lovex S065 | <<locked>> | 96% | 43,903 psi | 70% | 2379 fps | 95.6% |
| Norma 200 | <<locked>> | 80% | 51,735 psi | 83% | 2405 fps | 100% |
| Norma 201 | <<locked>> | 80% | 36,463 psi | 58% | 2234 fps | 97.9% |
| Norma 202 | <<locked>> | 80% | 36,535 psi | 59% | 2251 fps | 99.5% |
| Norma 203B | <<locked>> | 80% | 32,576 psi | 52% | 2198 fps | 95.3% |
| Norma URP | <<locked>> | 96% | 39,015 psi | 63% | 2372 fps | 95.7% |
| Ramshot Big Game | <<locked>> | 82% | 34,287 psi | 55% | 2254 fps | 95.5% |
| Ramshot TAC | <<locked>> | 82% | 41,771 psi | 67% | 2329 fps | 95.2% |
| Ramshot Wild Boar | <<locked>> | 80% | 37,971 psi | 61% | 2297 fps | 96.9% |
| Ramshot X-Terminator | <<locked>> | 80% | 42,496 psi | 68% | 2326 fps | 97.8% |
| ReloadSwiss RS 14 | <<locked>> | 80% | 25,846 psi | 41% | 1368 fps | 100% |
| ReloadSwiss RS 40 | <<locked>> | 80% | 44,077 psi | 71% | 2365 fps | 99.8% |
| ReloadSwiss RS 50 | <<locked>> | 92% | 46,804 psi | 75% | 2425 fps | 95.5% |
| ReloadSwiss RS 52 | 45.7 gr | 80% | 33,997 psi | 55% | 2283 fps | 95% |
| ReloadSwiss RS 60 | <<locked>> | 80% | 28,456 psi | 46% | 2162 fps | 96% |
| ReloadSwiss RS 62 | <<locked>> | 96% | 38,290 psi | 61% | 2385 fps | 95.2% |
| ReloadSwiss RS 70 | <<locked>> | 98% | 42,293 psi | 68% | 2451 fps | 95.2% |
| Rottweil R 901 | <<locked>> | 80% | 40,335 psi | 65% | 2283 fps | 99.8% |
| Rottweil R 902 | <<locked>> | 80% | 34,751 psi | 56% | 2192 fps | 97.4% |
| Rottweil R 903 | <<locked>> | 82% | 30,008 psi | 48% | 2149 fps | 95.2% |
| Shooters World Long Rifle | <<locked>> | 96% | 43,903 psi | 70% | 2379 fps | 95.6% |
| Shooters World Match Rifle | <<locked>> | 80% | 35,520 psi | 57% | 2257 fps | 99% |
| Shooters World Precision | <<locked>> | 80% | 32,953 psi | 53% | 2175 fps | 96.9% |
| Shooters World Tactical Rifle | <<locked>> | 80% | 46,528 psi | 75% | 2375 fps | 99.3% |
| SNPE Vectan BA6 1/2 | <<locked>> | 80% | 53,258 psi | 85% | 2162 fps | 100% |
| SNPE Vectan SP 10 | <<locked>> | 80% | 49,023 psi | 79% | 2448 fps | 100% |
| SNPE Vectan SP 11 | <<locked>> | 84% | 33,417 psi | 54% | 2238 fps | 95.3% |
| SNPE Vectan SP 3 | <<locked>> | 80% | 46,746 psi | 75% | 2369 fps | 100% |
| SNPE Vectan SP 7 | <<locked>> | 82% | 39,523 psi | 63% | 2300 fps | 95.2% |
| SNPE Vectan SP 9 | <<locked>> | 80% | 35,650 psi | 57% | 2241 fps | 96.3% |
| SNPE Vectan Tubal 3000 | <<locked>> | 80% | 38,276 psi | 61% | 2208 fps | 99.7% |
| SNPE Vectan Tubal 5000 | <<locked>> | 80% | 31,328 psi | 50% | 2090 fps | 99.3% |
| Somchem S321 | <<locked>> | 80% | 41,930 psi | 67% | 2356 fps | 99.1% |
| Somchem S335 | <<locked>> | 80% | 37,608 psi | 60% | 2208 fps | 99.9% |
| Somchem S341 | <<locked>> | 80% | 36,709 psi | 59% | 2254 fps | 96.5% |
| Somchem S355 | <<locked>> | 82% | 31,198 psi | 50% | 2159 fps | 95.3% |
| Somchem S365 | <<locked>> | 90% | 28,906 psi | 46% | 2182 fps | 95.5% |
| Vihtavuori N130 | <<locked>> | 80% | 43,410 psi | 70% | 2274 fps | 100% |
| Vihtavuori N133 | <<locked>> | 80% | 38,334 psi | 61% | 2208 fps | 100% |
| Vihtavuori N135 | <<locked>> | 80% | 33,576 psi | 54% | 2188 fps | 100% |
| Vihtavuori N140 | <<locked>> | 80% | 34,461 psi | 55% | 2192 fps | 99.4% |
| Vihtavuori N150 | <<locked>> | 80% | 27,731 psi | 44% | 2060 fps | 95.5% |
| Vihtavuori N160 | <<locked>> | 94% | 38,638 psi | 62% | 2329 fps | 95.5% |
| Vihtavuori N530 | <<locked>> | 80% | 39,073 psi | 63% | 2280 fps | 98.5% |
| Vihtavuori N540 | <<locked>> | 80% | 33,185 psi | 53% | 2182 fps | 98.9% |
| Vihtavuori N550 | <<locked>> | 94% | 37,594 psi | 60% | 2329 fps | 95% |
| Winchester 6.5 StaBALL | <<locked>> | 88% | 32,387 psi | 52% | 2172 fps | 95.3% |
| Winchester 748 | <<locked>> | 80% | 37,956 psi | 61% | 2320 fps | 98.9% |
| Winchester StaBALL Match | <<locked>> | 80% | 34,809 psi | 56% | 2244 fps | 96.7% |
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 96 powders for .338 RCM loaded with the .338 | 225gr | Sierra Pro-Hunter. ReloadSwiss RS 60 delivers the highest muzzle velocity at 2,674 fps; across all powders the maximum-charge window runs from 1,499 fps to 2,674 fps. Accurate 4350 gives the best case fill at 100 %, and 96 of the 96 powders fall inside the usable 80–100 % fill window.
Relative to the caliber's maximum pressure (430 MPa), the top charges use 56–90 %, leaving at least 10 % headroom. The 225.0 gr projectile in 0.338" calls for a 1:15.5 twist; slower twists will usually not stabilise this weight. Accurate 4350, Alliant Reloder-16, Alliant Reloder-17 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. Alliant Power Pro 2000-MR, ReloadSwiss RS 52, Hodgdon CFE223 rank at the top here: for .338 RCM with the .338 | 225gr | Sierra Pro-Hunter they combine a high case fill with complete burn and sit in the upper velocity band. Always begin at the start load and work up in small increments while checking case and primer for pressure signs.