I tried hand tightening the aluminum barrel nut from my Mk4 rail on to the upper receiver… It would go on about 1/2 a turn then no more. Didn’t want to force it. I tried two standard barrel nuts after that and both went on fine. I also tried the Geissele nut on another upper receiver and it went on just fine… Is it a spec issue on my Upper? If so… why would all the other barrel nuts (and a KAC URX 3 rail) go on just fine?
Anyone have this issue?
I sent an email to Geissele so hopefully they will have some ideas.
Not to ask a dumb question, but how careful were you when trying it on the first upper? I’m trying to remember what the inside of the wrong end looked like, but I remember when I was installing my MKII thinking that both sides of the barrel nut looked very similar except one was threaded all the way through and the other was not threaded. I just can’t remember if there was anything on the other side of the barrel nut that might catch the threading at all and cause that problem.
I had an extra upper and barrel and Geissele nut laying around and tried a few things. The back side of the nut will not thread on the upper. It just spins. The threaded side of the nut when properly installed will be almost flush against the upper… almost. (BCM upper and barrel). I purposefully cross threaded it on the upper and got about one half turn before it binds. A good way to make sure the nut is catching the threads is to… Before tightening it on at all, push the nut to the upper and pretent to loosen it. You will feel the nut kind of click when it comes off the last thread. Then start to tighten. This assures its flat on the threads before tightening. Just what I do to make sure it’s not cross threaded. Also inspect threads on both nut and upper for a bur or something inbwtween the threads.
I was able to get the nut on. It was just very tight and would not go on by hand. It required the barrel nut wrench and a bar. But with a little leverage it went on OK. Did not bind or anything. It was just on there super tight.