[Effects of cold and heat on ammo performance?]

I live in southern Ontario which is across from Michigan and many years ago started out using Win231. In the cold weather my pistols (38's) would lock up as the primers were backing out when fired. I did some research to discover this was caused by the very cold weather. Checking on the Wire at that time I found out many of the shooters in the cold weather recommended using Titegroup as it was NOT cold sensitive. This included Positive accounts from Deuce Stevens and several other top shooters from Michigan. I switched to Titegroup and haven't had a problem since. I can see where the amount of powder used will make a difference as others have stated. YMMV !