The search feature doesn't seem to be full up just yet and I don't have time to re-create the post. However, Stan Watson did a the most scientific test I have seen on this topic several years ago and published it in his reloading book. Stan used a 30-06 with a 165 grain bullet and an Oehler 43 PBL to gather his data. He tested at propellant temps of zero degrees, 70 degrees, and 110 degrees.
With standard primers, IMR 4350 had a 63 fps increase between zero and 100 degrees, VV N-560 had a 51 fps increase, WW 760 had a 57 fps increase, and H4350 had a max variation of 5 fps, and the 70 degree load was 5 fps faster than the 110 degree load.
I think if a guy has worked up his load properly--which means using the most consistent load vs the one-time best and not using a hot load, the sweet spot ought to be big enough where a 63 fps difference in velocity wouldn't meaningfully change the POI or group size out to 500-600 yds. Of course, the only way to know for sure is to actually check the load under various temperatures.
I think the relative "hottness" of the load, the speed of the powder, the condition of the barrel, and the chambering itself will have a large play in how much velocity increase or decrease one would see as the temperature changes. I would speculate that a 375 H&H loaded with a 270 grain bullet at 2650 fps would be much less sensitive to temperature extremes than a 300 RUM shooting a 220 grain bullet at 3200 fps. I also think that as the the load gets hotter and hotter, small changes in propellant temperature will have larger and larger effects on pressure and velocity.
I do not know of anyone who has done a complete enough test to fully check this effect, but it would be fun to have enough time and resources to do such a test.
In most cases, I think lot-to-lot consistency of a powder probably is a bigger concern than than the actual level of sensisitivy to temperature. In my experience, Hodgdon Extreme powders seem to have very good lot-to-lot consistency.
Last edited by Blaine; 02/11/07.
