My experience has been the Fio 616 (209 type) primers are larger than Win/Rem/Federal and that switching back to Win/Rem/Federal after using Fio's resulted in a bunch of loose primers and powder in the bottom of my shell bag. I have read the are straight sided and the amercan primers are step sided so after using a Fio the US primer would not be holding on by much. Other than that they seem to work fine. If you Google Fiocchi primers and cold weather you will see some reports on duck hunting chat.com, trapshooters.com that people report issues with cold weather use.
http://www.duckhuntingchat.com/forum...?f=14&t=125799
http://www.trapshooters.com/cfpages/...05&Messages=16