I've learned to store ammunition in a cooler to protect it from heat and cold. Summer heat is worse problem here, of course, but cooler weather also causes change.

Jason,
Yes, I have found that heat and cold will change the size of the group from ammo. I can take a brick with me to a match and if it is exposed to extremes in temp along the trip that brick will not group the same as another from the same case lot that has not been exposed to temp extremes. For that reason, like many of the shooters, I tend to insulate the carry case that I have for the ammo, and do my best to see that it is not exposed to extremes in temps.

Mary

Just a little off topic but related, does anyone notice a change in poi if they move the front rest to differnt positions on the forearm? I can place the rest towards the front of the forearm and get one poi and if I move the rest further back, say where your support hand would be I get a totally different poi, not that far off from the other but different.

Shakes,
If your npa is high, move forehand forward, or lift butt in your shoulder and so on.....so in answer to your question yes the poi is different.

Mary

I have seen the same thing, Matt. I usually remove the foreend stop from my front rest and try to place it as close as I can back to the triggerguard where my forward hand rests as possible. Be careful, though, the barrel of your rifle will be heavy enough to make the rifle tip forward if you let it go expecting it to just sit in the rests that way.

we're going off topic here, but....

it also has to do with the amount of flex and tension being put on the receiver / barrel. the further back you put the rest to the meaty part of the receiver, generally the better the groups. you can see how far back i have the bipod mounted for that reason...