This very common with some lowers when used with the NM 2 -stage trigger. I only use WOA tuned RR NM 2-stage triggers in my builds and in all three of my LR-308 lowers and one Olympic lower, the bolt carrier hits the top of the hammer and prevents it from being pulled back. However, on all of mine I can pull the carrier back about 1/4 to 1/2 inch before it locks up so before doing what I am going to tell you to do make damned sure that is what is happening on your 416 also. See note below***
I called RR about the problem and they said to take a trigger stone or other fine stone and remove about .003 to .005 inch from the highest part of the hammer in relation to the top of the lower as you would see the hammer in the cocked position. Take your upper off and cock the hammer. While the lower below is an LR-308, the procedure is the same for any AR lower.
See how the very tip of the hammer extends up from the lower in the cocked position?
Measure this height from the top of the lower to the highest point on the hammer:
Then take a stone and run it parallel with the top of the lower and stone off about .003 inch off the highest point on the hammer and try again.
You only want to remove enough to let the carrier operate freely but on one I did have remove a lot more than .005 inch. I had take it down about .015 inch on the Olympic lower to make it free the carrier up. This is not a problem since it is not the tip of the hammer that hits the firing pin; that occurs much lower on the hammer. But if you remove too much then the carrier will not push the hammer down far enough to catch the sear or disconnect. And once done it does not mean that if you put the trigger on another upper that it will work on it also, but so far I have not encountered any problems but I have also not put another upper on the Olympic, the one that needed more than .005 inch removed.
Just make sure that this is the problem before you start stoning any metal off the top of the hammer. It cannot be put back on.
To test, assemble the upper to the lower and gently try to pull back on the CH. The bolt carrier usually moves a little before locking up (it compresses the hammer fully and bottoms out, forcing it will damage the trigger so don't do it!).
Use the FA to push the BC forward again and push out the rear take-down pin. Holding the upper firmly against the lower, pull back on the CH and you should feel the carrier contacting the hammer and push it upwards a little bit.
If you pulled the carrier back too far in the past and locked it up and had to cuss and pry to return it forward, you pretty much have your culprit, it got locked against the top of the hammer.
***Now, the fact that you said your BC does not move at all has me concerned. That sounds like the back of the carrier is hitting the buffer tube and there is misalignment there. Check that to make sure before you take the stone to anything. If that is the problem I have no suggestions for a cure.