I started using R-22 for my 300WM and although I like the results I'm getting I didn't like the idea of a powder that is temp sensitive. I switched to H4831 and H1000. Out of thoes 2 H4831 shot the best .336 to be exact, but H1000 was not far behind also with sub .5 MOA. My issue is with a load of 72.5g of 4831 there is alot of "air" or open space when I seat the bullet and I believe this is the reason I have a high ES like 90fps. A friend of mine suggested using IMR 4831/4350. Is the IMR line of powder temp sensitive like the R-22 or more like the "H" line of powder. I did notice that IMR shows a little faster load than the "H" line.