They are horrible since nobody can ever spell Fiocchi right! I won't use them in cold weather. They have been very inconsistent in a wide variety of loads with many powders in lower temps. Not too bad in mild weather in most loads. I would not recommend loading a lot of one load until youy have been able to test them at cold temps. I usually put a half box in the freezer and keep a half box out. I'll fire them over a chronograph while still colad and fire the room temp ones as a comparison. It's been an eye opener. I do the same with many other primers and loads. The Fiocchi 616 seems to be one that does poorly. I can't say anything about the Fiocchi 617, since I have not yet tested any. I didn't have enough of the 615s to worry about testing any.
Ditto OZ, in fact I have had a problem w/ them falling out while reloading which is why I quit using them. Too much bother to seperate my empties by what primer was in them. I also think they burn dirty.
While the coldest weather I've used them in would be the 20's with no ill effects, as well as up into the 100 teen's, which were fine as well, I can find no problem with them in STS, Estates, and Feds. I've probably used 15 or more sleeves of them and have no problem using Cheds in the same hulls. The only hulls I've noticed loosening after three or so loads are the Estate/Wally paper based hulls, and that would be with either Fiocchi or Cheds. However if it makes one feet better to pay 50% more for the "big three" primers, then go for it. No question I would be with Wins (USA made) except for the price, but there is a limit to loyalty when it comes to that much difference in $$.
loaded at least 10,000 of them in federal papers. There bigger in diameter as mentioned so once you load a hull with them you don't want to go back to another brand. Other than that I've not had a problem.
As far as size, my measurements show the 616's to be the same as Cheds and Wins. There was a time back in the 90's when they were in fact a few thousanths larger causing the problems described above. At present that is no longer the case. I'm using a decent dial caliper and a mediocre micrometer, but they do agree and Wins or Cheds don't fall out (nowadays) after using the Fiocchis.