Trying to decide between the Geissele MK8 and the KAC URX 4 m-lok rails? Anyone used the KAC? I know the Geissele has a pretty badass barrel nut setup. How does the KAC compare?

Any others to consider?

I've used the Geissele rail before and really like them. The other ones that I really like are the Midwest Industries M-Lok rails.

The one thing that I really don't like about the URX 4 compared to the older URX rails is that you shim the whole rail system against the receiver.

G rail, hands down.

I really like the Geissele rails.  They have a very solid lock up.

Geissele, for sure.

The Geissele will likely be an easier install, although both come with the necessary wrench. The gas block is the tricky part on the URX4, but Ayan from boltcarrier.com showed (in the KAC forum) that standard gas systems (i.e., carbine, mid) are not an issue in this regard.

You really have to hold an URX4 to appreciate how solid it is. I was very surprised and have no doubt it would hold up to hard use.

For me, the URX4 is more aesthetically pleasing, but beauty is in the eye of the beholder. I think the Geissele handguards are sweet, but am always put off by the fact that they don't put mounting points all the way around the handguard (i.e., 4:00 and 7:00 positions). There may well be a reason for why they do that, but it kills me nonetheless. I had a sweet 13" Mk1 in DDC and dumped it because I couldn't get over it. I would probably jump on one if I could ever find a first-generation one.