So I finally put 300 rounds through my FN right out of the box at the range on Saturday. The magazine springs must have just been stiff as hell straight from the factory, because spending 3 weeks with 15 rounds in them definitely made them infinitely easier to load. My CAM loader, while somewhat finicky, was able to jam all the ammo in without a problem given that the first round was correctly aligned.
The only thing I found was that I had one failure to feed. I think maybe the mags are a little goofy. The gun never locked open on the last round like it's supposed to. I'm thinking something is wrong with the magazine followers. That or the ammo is just not cycling the slide far back enough for the slide stop to catch. Or, most likely, my hand is preventing the ambi slide release from adequately catching.
Otherwise, it's a great shooting gun. The sights are very hard to pick up through my dripping-fog (I was sweating my ass off) Aegis shields, but I was getting some great, spot-on accuracy when I really concentrated. I need to work on precision and "anticipation fatigue". I found that with 15 rounds, the last five I'd start shaking up when anticipating the shot. I have a good video confirming this too.