SD mentioned this to me, but honestly, I wasn't sure what he meant at the time Well, now I know.
I took my M4 to the range for the first time and shot 100 rounds. Before I went, I took it apart, cleaned it and installed the FFT handguards. It was all new to me so I didn't even pay attention to the barrel fit (maybe it was perfect, maybe it wasn't). When I cleaned it after the range session, I noticed that the FFT handguards do not allow me to push the barrel all the way in. No gap with OEM parts, but a 1/16? of an inch with FFT. I got a bit concerned. After taking them on and off a few times and trying different things, I just pushed down on the barrel while tightening the plastic mag tube nut and it seems to be fine. I am a bit paranoid now. I can't tell if the gap is there or not. If there is one, it's tiny.
Update: Just looked at it one more time. To an untrained eye, looks fine, but when I hold it against some back light, I can see a small gap in the silhouette bit enough to fit a piece of paper (maybe two)
Not sure what to do now. Please offer your thoughts