have you thought about using stripper clips? or would that cause more hassle
I've used the FNC1 in the past in Actic conditions with steel mags and never had the problems you speak of?? Make sure in cold times, all the oil from the inside is removed, and if you need some lub, use graphite in powder form. If you can, leave you mags out in the cold, and don't bring them into the warm (when you're hunting that is). The same goes for the rifle if possible.
That sounds like a good idea, if you use the short 5 round mags, they wont protrude much and would hopefully stay clean and free of dirt/snow.
those short "parade" mags are far more trouble than worth- there's nothing to grab on to , ( which you need changing mags) they don't home in properly right out of the box, ( or at least the 4 i have don't) and they sometimes need a screwdriver as a prybar to change- moreover it leaves the mag change lever.button exposed and COULD BE BROKEN- in short, go with a pinned 20 round and don't look back- mine don't protude at all, but they're springfield armoury