Author: britrifles
Subject: IMR 3031 load data (replicating 303 Mk. VIIz)
Posted: December 27 2024 at 4:21am
Subject: IMR 3031 load data (replicating 303 Mk. VIIz)
Posted: December 27 2024 at 4:21am
 ProudAussie wrote:Thanks heaps for the helpful replies! britrifles, thanks for the information regarding powders. I have read before that AR2208 is a good powder for reloading 303, and now that you've mentioned it I may consider using that instead. Just a quick question for you: what exactly are the benefits of having lower pressure? Is it to do with protecting the rifle, or something else? Also, thanks for the heads-up on the Sierra bullets. Sounds like I'll give them a try when the time comes. Thanks again, William |
William,
Lower chamber pressures give longer life out of brass cartridge cases, less wear and tear on the action and longer barrel life. Even small reductions in chamber pressure has measurable benefit. No. 4 rifle production ended in the 1950’s, and new barrels are difficult to find and expensive.
It would be helpful if we knew exactly what you are wanting to achieve. If you want to exactly match the original ballistic performance of the Mk VII cartridge, you will really need a chronograph. You can get close by interpolating the reloading data tables to obtain the charge weight that gives a muzzle velocity of 2440 fps with a 174 grain bullet.
40.0 - 40.3 gr AR2208 (VARGET in the US) with 174 grain Sierra MatchKing will get you very close. The trajectory will match the Mk 7 out to 600 yards. Beyond that, the higher BC of the SMK gives a slightly flatter trajectory. It’s also a very accurate load for the .303, I’ve found none better in years of loading the .303 for competition shooting and have shot in excess of 10,000 rounds thru numerous No. 4 rifles.
Probably the second best powder I have used is Re15. It gives excellent accuracy with similar pressure as AR2208 loaded to the same muzzle velocity. IMR 4064, Norma 202, VV N140 are other good choices in the same burn rate range.
IMR 3031 is a faster burning powder, it gives higher peak pressures for the same muzzle velocity. As you have noted, there is not a lot of published data with a 174 grain bullet, 3031 is more suited to lighter bullets (125 and 150 grain).
Having said that, I have tried 3031 with 174 grain bullets, and it can be safely loaded to 2440 fps muzzle velocity, buy why use it when there are more suitable powders that give lower pressures and better accuracy?
