Several "F" class and bench rest shooters have told me, that H4350 shoots much better in 6.5mm, than IMR 4350. The H4350 IS significantly better in my 6.5x55. Since no one here has apparently compared the two 4350's, except Craigster, I may have to try it, and see which makes my Krag happier. It is curious, that all three 4350's have about the same burn rate, and some even say they are interchangeable (I would not try that), but in the 6.5mm H4350 delivers much different accuracy. If I do make the comparison, I will let everyone know. I may not get the chance until warmer weather.