John, so far I've not noticed the lot-to-lot variation with the IMR as I experienced with the H-4831. You are of course correct on the sensitivity issue and IMR & H-414, but I will offer this; I used my 375 H&H in Africa when the temps were in the low 100s in September and two days ago (when I first posted) I shot the same rifle/load up here at our place in the PA mountains where the temps were in the mid-30s and velocity was on the button at 2550. Also, when I do my load testing in hideous, hot, muggy Florida :), I try my loads when the temps are in the mid 90s for that very reason. Lastly, the two most popular powders in doubles are IMR 3031 (alsmost but not quite a one for one swap with cordite) and RL-15.
Today I just finished regulating my new 375 H&H Flanged magnum (it was regulated at the factory with Norma PH ammo w 300gr Woodleighs @ 2395 fps) and it regulated well both with Woodleigh and Hornady 300gr Bonded bullets, the best and most consistent powder (SD 9-12 fps) was IMR 3031. BTW, Norma does have load data on their website using RL-22 and UNP (?) no clue as to that powder and the rifle does shoot ok with them but IMR 4831 was the best, right at 2425 FPS BTW.
jorge
PS: Aussie, your post is noted, that is why when working loads for double rifles, I regulate to velocity and if I match or get close, the rifle regulates.
Last edited by jorgeI; 04/25/24.
