I have loaded and used both forms of 4350 powders. Both will work in the same cartridges but the load data is not interchangeable. In my experience, H4350 is a little faster than IMR4350. In my .30-06 based rifles (25-06, 30-06, 270 Win) IMR4350 seems to provide better accuracy results. In my .308 based rifles (.243, .260, .308) H4350 seemed to get better accuracy. As eluded to in a previous post, I get equivalent velocities with less H4350 powder in the case when compared to IMR4350. My .25 WSSM loves H4350 and kinda likes IMR4350. Both will work, but I will stick with my 1/2" or less groups from the H brand when compared to around 1" groups from IMR.