I've observed the same effect with IMR4350, with flattening of the MV slope starting at 78 gns. Just noted in my reloading notes that with RL-19 the MVs are ~ 200 fps lower when compared to equal weights of IMR4350. So I guess I have some work to do with a fairly narrow range of burning rates between the 2 powders. Should be an interesting Summer with the chrono.
I found exactly the same thing in my Norma with RL15 and 225 grainers. Big Game beats it by at least 200 fps.
