I just recently go into the FNC game after wanting one for quite some time. Heres what I have found out in my research on an absolutely awesome rifle.
Originally FN released the rifle as the FN CAL, it looked similar to the FNC, however the gas system was much more complex, and the ease of build and field stipping was too extreme for it to be competitive as a military arm.
FN went back to the drawing board and came out with the FNC a few years later.
Eventually the FNC was adopted by Sweden, Belgium, Congo, Venezuela, Tongo, El Salvador and Sri lanka. and in the PINDAD SS1 form Indonesia, Cambodia, Mali, Nigeria, and the UAE--with some of those countries simply exporters/and some not quite fully adopting it.
Essentially the FNC is what happens when the FAL, AK, and AR have a gangbang.
It takes AR mags.
Uses the Operating system of an AK (Long stroke piston, rotating 2 lug bolt)
Had the Ergonomics and furniture styles of a shortened FAL, and a very simply gas regulating system similar to an FAL.
From what I understand 6000 were imported into the US, 5000 of such being the folding stock para model. with either a 16" or 18" barrel
1000 of them were imported with the rare fixed stock, with 18" barrels.
More transferrable sears were imported than rifles, which made the FNC a very cheap Machine gun to get into. In fact the semi auto ones have become rarer than the machine guns.
With the awesomeness of cheap machine guns, comes the need for parts. So unfortunately much of the surplus parts have about dried up.
For the semi auto ones, about the only thing that really breaks is the firing pin. Luckily you can buy after market firing pins in many places, DSA for example has them.
I love mine, but there are a few things that are odd/different/outdated about the FNC.
1. The trigger pull is as heavy as a truck, but very predicatable and crisp.
2. I have Yuuge hands, and the safety is still out of reach of my thumb.
3. The recoil is something that has to be experienced, it is very, very light, by almost hydraulic in nature.
4. It has no bolt hold back function at all.
5.The barrel is 1:12 twist, evidently a few made it in with 1:7 twists but they are rare. However that being said, mine is stupid accurate for the rifle style it is. (Iron sighted fighting rifle)
6. No built in picatany rail for optics (Stormwerks took care of this issue)
7. Mine takes all mags, but some magwells are too tight for polymer mags
The Swedish version, the AK5a/b/5c is "advanced" in a few ways
1. Different hand guards with a slimmer more textured profile.
2. Folding stock comes in short or long for the ak5ab, the ak5c is adjustable for length. with new design.
3. Pistol grip got a less extreme angle, and a more flared bottom edge
4. Charging handle went from a roller look, to the anal bead
5. rear sight was changed to allow for easier adjustment, front sight became folding on the 5c.
6. Built in rail for optics
7. Purpose built polymer mags (fragile by report)
8. 1:7 twist barrels.
9. Bolt hold open made possible.
10.Green in color coating vs.Black
11. Larger Trigger Guard to allow for use of gloves.
12. Ambi Safety.
13. Pronged flashhider for the 5c.
Overall I love mine, its a truly unique part of my collection. I have enjoyed over the last few months locating some spare parts and such. The original imports came with all of the goodies, now even finding the original sling can be a pain. It also has its own little tool for cleaning, where once to be very available..now goes for 80 bucks.
Hope this helps. Here is mine.