Re: tempature and point of impact and powder?
I'll add to what Budlight was saying, in that the rifle temp, air temp and BP are the variables if you keep your ammo a consistant temp.
30 degrees could mean a 3/4 MOA POI shift possibly. You will only "know" from logging the data and examining it though.
To throw a wrench in it... you might find that POI can actually be higher with a cooler temp, if your ammo is allowed to stabilize at the lower temp.
I think it is just easier to completely eliminate the ammo temp / MV / barrel harmonics variable. Left are the temp, BP, wind, range and angle variables, which are all pretty easily dealt with though.
If the sun is beating down on one side of your barrel in the morning, then the other side in the afternoon, how much left-right POI shift will result if ambient temp was +100 deg F? What if the sun is directly overhead, but then the clouds roll in and the barrel then evens out in temperature with the underside?