Proof that temp changes can affect your patterns...

[mightyjoeyoung]

Shot the SAME load/choke/lot out of my 20 gauge 870 today.  The last time I shot it was 70 degrees, sunny, and basically just beautifull weather.   The $ed. HW 7s put up an avg 150+ at 40 yards though the jellyhead .570 on a 21" highly pollished and cleaned barrel.  Today, it was nasty, chilly...40 degrees and high humidity.  The patterns while reasonably even were HORRIBLE compared to the 70 degree weather.  Nothing changed but the weather conditions and my patterns were about half as dense.  Btw. I also shot the PG .570 I just got.  My gun/loads don't seem to like it at all.  Ill have to recheck it when it warms back up and I get the chance to run a bunch of spoiler rounds though it...

[SumToy]

One thing I know that a FEW think is wrong may help. In the cool air the barrel will get damp after it is fired.  The alcohol will dry it out.  It may have been what got you. 

[mightyjoeyoung]

One thing I know that a FEW think is wrong may help. In the cool air the barrel will get damp after it is fired.  The alcohol will dry it out.  It may have been what got you. 

Thought about that too, but I let the barrel cool completely between each shot and then clean with a bore snake soaked in a little carb/choke cleaner that eveaporates quickly, leaving the barrel squeaky clean.  Ki take my time when patterning.  Never get into a hurry as it one of those relaxing things for me to do on my days off.   

[HuntSource]

Mighty,

Yep, I, too, have found weather can dramatically mess with patterns. That's why I sometimes question why there's so much "lot love" for ammo. I don't disagree that some lots are better than others and I'm a big fan of the OWs. However, climatic conditions are a much bigger deal than lot #s. My guess is that much of the presumed lot variance is actually due to differing weather conditions when the patterns were shot. I've seen shells from the same box of Hevi-13, 12ga, 3" 2oz, #7s drop by nearly 100 in the 10" ring @ 40yd from excellent to poor weather conditions.

HuntSource

[ILIKEHEVI-13]

Yep I know all to well what cooler temperatures will do to a pattern.  I seen my best shooting choke the Star Dot for my 835 that shoots lights out in 70 degree weather shoot just mediocre patterns at 45 degrees. 

[Philippe]

I've noticed that myself, when i started working on both of my turkey guns back in late Feb the temps were in the 38-42 range and the patterns were just ticking me off. Now that it is up in the 72-78 range things have made a major change. It seems like the more it warms up the tighter these patterns get.