Re: tempature and point of impact and powder?
Kind of surprising that you have that much variation w/ H4350; it is supposed to be one of Hodgdon's 'Extreme' powders produced specifically to be temperature stable. AFAIK, Varget, H4350, H4831SC, and H1000 are all supposed to be. Varget I can vouch for, is pretty dang temperature stable. Not completely unaffected, but noticeably less so (in my guns) than say, the Alliant Reloader series, or other such as IMR 4064.
Vihtavouri powders are supposed to be kind of middle of the road, Ramshot powders are specifically billed as being temperature stable (though more than one person has determined that Tac is less stable than say, Varget, but comparable to RE-15).
I believe more manufacturers are making some sort of effort to minimize temperature sensitivity of their powders as that is what shooters today expect and are wanting. Like I said, generally speaking Hodgdon Extreme and Ramshot powders are more so than most. Even so, to be responsible about it, if you want to play around shooting at long range in widely varying temperatures, you need to test your loads under said conditions. Take your loads to the range in a cooler w/ an ice pack in it in the summer, and see what a chilled round does in your gun. Similarly, take some rounds to the range in the winter, stick them in a snow drift, and then shoot them. Take some others, and set them over the defrost vent in your rig, and heat them up to 90+F, and shoot them. Check the velocity of each. All kinds of data you can accumulate if you want to spend the time [img]images/icons/wink.gif[/img]