Thanks guys, u saved me a ton of work. I'm now leaning towards the Centurion c4 cutout rail. Can anyone confirm if this will work on the 6920?
Just make sure you get the carbine cutout rail not the midlength. I see they also offer gas blocks, what exactly are these for and will I need or want it?
You have a fixed front sight already (that's where the gas tube is anchored above the tiny port hole cut in the barrel). There's no need for a gas block. If you wanted a continuous rail, you would shave down the existing front sight and mount the rail over it. In that case, you would no longer want the cutout rail.
Also looking to add a eotech Xps3, troy BUIS, Magpul grips, and magpul ctr stock.
If it were me, I would consider firing the weapon as is before adding too much furniture. I would say the Troy would be very suitable, but the other stuff might change with research and experience with your weapons. The optics choice has always been simple for me when it came to red dots. I think they are stated nicely here. Then again, since I don't know your design intent for this build I can't say a Red Dot is even the right choice. If you're keeping it simple the carry handle sights may be all you want after some range time. As for the grips, same advice. Research and understanding design intent will carry you a long way. More rob_s love, but this video explains some pros and cons of some of the more popular options out there. My hands are not as big as Rob's and for that reason I went a direction that would make no sense for a guy with big hands.