100 yard groups from my inch fal (L1A1) are 4" wide by 8" tall when feeding from a magazine. Nice round 4" groups when single loading. Headspace is okay, but... After reading here and at "fal files forums", it looks like some kit guns (like mine) have sloppy lockup between the bolt and carrier at the upper rear section so when you use a magazine to feed it, the spring tension changes as you go through the 20 rounds and that slightly changes the way the bolt is angled when fired, which causes vertical stringing in your groups. I've recently found a couple of extra bolts and carriers though and I'm gonna try switching them around to see which combination gives the tightest lockup with the carrier for the least stringing. A few people have also tried welding a little material into the bolt carrier, and others have tried putting a set screw in the same spot to keep the lockup with the bolt even. I'm hoping I won't have to resort to that sort of stuff. At this point, I'll just be happy if I can stop the stringing. I don't really like the idea of living with 4" groups either, but that's better than 8x4.
This doesn't seem to be a problem for new fals like DSA, etc. Just some of the old kit guns.
Hope you get one that's better than mine.