4th rail switch, potential upper receiver issues?

AR/M4 AR Technical Discussion
1

Hey guys, I’ve got a simple, quick question. I’ve switched the rail on my 6920 3 times already, but was kicking around the idea (in the effort to save money) of installing the Geissele MK1. I’ve had the DD RIS II FSP, DD RIS II, and it’s currently got the KAC URXIII that is ok, but limiting. I’m not adverse to building another upper, but don’t have a need and I’m trying to keep my “arsenal” slim. Would it cause problems to take off the URX and install the MK1? If so I’ll just build another upper.

Thanks,
Mate

2

So what is the issue or why have you swapped out 3 other rails?

3

I’m worried that the torquing to install the barrel nut will cause stress on the upper.

I kept switching to find an optimal set up, did’t like the other options and the MK1 wasn’t available at the time. Found one at a steal and now I’d like to use it. I don’t need two 16" uppers, but if it’s going to cause problems then I’ll have to build another.

4

I had an indexing pin on a barrel from a very well respected manufacturer come loose from swapping stuff around too much.

5

I doubt it. I have an upper that has been barreled/rebarreled several times over the course of many months in my classes. As long as you do use the correct tools.