Every year at the beginning of winter, the Technoid reminds you to set your clocks back and increase your powder charges. Cold weather slows down your shotshell. The rule of thumb is that if you have been shooting 2 3/4 dram 1150 fps loads, switch to 3 dram 1200 fps loads to stay even.
Ted Knapp was kind enough to perform a 0F and 70F chronograph test on various shells. Using once fired Remington Premier hulls, all Remington components, 1 1/8 oz of shot and the #31 MEC bushing dropping IMR 700-X (about 19.0 grains), Ted chronographed 1205 fps at 0F and 1244 fps at 70F, a difference of 39 fps. Using the #33 bushing (over 20 grains) he chronographed 1246 fps at 0F and 1302 fps at 70F, a difference of 56 fps. Factory cartridges from Kent in Britain chronographed 1290 at 0F and 1338 at 70F, a difference of 48 fps. All chronographing was done in five shot strings.
Ted went even further and shot for uniformity, at a constant temperature, a box each of Remington factory loads, the Kent factory loads, his own reloads in once fired hulls and his own reloads in 4-5 times fired hulls. He found that his own reloads in once fired hulls were the most consistent with an average variation of about 10 fps, that the Remington factory shells had one or two variations of 25 fps and that the Kent cartridges had several variations in excess of 50 fps. He also noted that his 4-5 times fired reloads lost about 25 fps when compared to his reloads in once fired hulls, but they remained consistent.
Ted was very wise to stick to factory wads for his winter tests. Some of the clone wad companies use recycled polyethylene, instead of the virgin compound used by the majors. Depending on the mix of the recycled plastic, the wads can harden in the cold and produce bloopers. In winter, buy the factory stuff.
While we are at it, many shooters also occasionally go up one pellet size when it is cold. Frozen targets are harder to break than warm ones.
Bottom line: when shooting in the cold, use a slightly stronger shell in order to maintain performance.